Abdominal plates,spiracles and sternites in the ventral mesosoma of embryos of the desert scorpion Paruroctonus mesaensis (Scorpiones,Vaejovidae)

Summary

The scanning electron microscope was used to study changes in the ventral mesosoma of the vaejovid scorpion, Paruroctonus mesaensis. Observations are compared with those from scorpion fossils. The oldest fossils are from the Silurian period; migration from water to land occurred in the Carboniferous and Permian periods. All recent scorpions are terrestrial with four pairs of booklungs and spiracles in mesosomal sternites. Ancient eurypterids and scorpions had flap-like abdominal plates attached to the ventral surface of five mesosomal segments. The abdominal plates were apparently an aquatic adaptation, and authors have described possible gill tissue in the chamber above. In scorpion embryos, rectangular (holostem) plate-like structures precede the formation of sternites in the ventral mesosoma. Transverse folds were seen in the space above the abdominal plates. The lack of elaborate gill-like structures here supports an earlier hypothesis that aquatic scorpions had other mesosomal respiratory sites (e.g., pectines), resulting in less reliance on respiratory tissues above the abdominal plates. Spiracles initially appear as round or ovoid patterns in the epidermis at the latero-posterior margins of the ventral plates. The booklung spiracles are positioned farther anterior in sternites, but the developmental sequence for this transition is still unclear and may occur later than the stages of this study. The abdominal plates lengthen and enlarge laterally and/or epidermis is added at the lateral edges so that broad, overlapping sternites eventually cover the ventral surface of the mesosoma.     

Matrotrophic adaptations and early stages of embryogenesis in the desert scorpion Paruroctonus mesaensis (Vaejovidae)

Light and electron microscopy were used to examine the sequential changes in embryos and maternal reproductive tubules in the vaejovid scorpion, Paruroctonus mesaensis. The early stages are described, from oogenesis to the time of embryogenesis just before spiracles and booklungs begin to appear. The oocytes and associated trophic cells originate in the epithelium of the maternal ovariuterine tubules. Each oocyte with follicle (primary trophic) cells forms a protuberance on the tubular surface. After fertilization and cleavage, the morula appears to be pulled into the tubular lumen by tissue invaginated from the wall opposite the protuberance. Secondary trophic cells originating near each oocyte form a trophic layer parallel and connected to the ovariuterine tubules. These cells encircle the tubular epithelium and apparently induce or transform it to a trophic mode. Within the tubules, each embryo develops in a specialized region (uterus) where the embryo abuts a cell mass (follicular placenta). The latter, along with the tubular and uterine epithelia, apparently releases nutrients that are absorbed through the embryo epidermis. The main structures of the embryo body develop from the germinal disc of the blastula. Segments and appendages are formed in an anterior-to-posterior direction. The chelicerae, initially posterior to the stomodeum, are gradually positioned anterior and dorsal. The early abdomen has only a few segments with no separation into meso- and metasoma. The latter structure, when formed, has a ventral flexure and segments of smaller diameter than those in the mesosoma. The telson starts as a broad, bilobed structure, becoming tapered with two openings near the tip. Each pectine appears first as a lobe attached to the body wall. Transverse grooves appear distally and then later along the entire length. In the stages of this study, there was no indication of ventral plates, gills, or sternites in the ventral mesosoma where booklungs and spiracles will eventually form. J. Morphol. 237:187–211, 1998. © 1998 Wiley-Liss, Inc.     

An Angiocardiographic Analysis of the Central Circulation in the Air Breathing Teleost Channa argus

The unique anatomy of the double ventral aorta outflow system in the air breathing teleost Channa argus (Ophiocephalus) showing an anterior and posterior ventral aorta is described. The marked trabeculation of the ventricle and bulbus arteriosus and the arrangement of central veins are used as a basis for the hypothesis that Channa may selectively channel the well oxygenated blood draining the air breathing organs via the anterior cardinal vein to the posterior ventral aorta, which forms the systemic arterial circulation. An angiocardiographic technique was used to test this hypothesis, as well as to delineate the functional role of the heart chambers in the cardiac cycle. No reflux of contrast to the sinus venosus during atrial filling and no ventricular filling before atrial contraction were apparent, which makes the atrium the main determinant of the ventricular end-diastolic volume. Ventricular contraction left a small or no residual volume. The ventricular ejectate was initially nearly completely absorbed by the very elastic bulbus arteriosus, acting as a pressure chamber (Windkessel) stabilizing and prolonging ventral aortic blood flow. Contrast medium was not selectively passed from the anterior cardinal vein to the posterior ventral aorta. However, the diameter of this vessel and its density of contrast were greater than in the anterior aorta, suggesting a preference for a greater blood flow from the air breathing organ through the heart to the posterior aorta.     

A new species of scorpion of the genus Neoscorpiops Vachon, 1980 (Scorpiones: Euscorpiidae) from India

A new species of scorpion of the genus Neoscorpiops Vachon, 1980 is described from Northern Maharashtra. Neoscorpiops maharashtraensis sp. nov. is a medium-sized scorpion species ranging from 36 to 42 mm. Carapace, mesosoma and metasoma brown, legs and telson yellow; pedipalp in a shade of brown with carinae dark drown to black. Granulation on carapace coarse, with a few smooth patches; on mesosoma, which is restricted to the posterior half. Anterior margin of carapace with a moderately deep “U”-shaped emargination medially lacking elevated edges. Pectines well developed 7/7. Trichobothria on patella ventral 13–16. Pedipalp chela narrow and elongate in males, length-to-width ratio in males is 4.86–5.05.     

Effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide in rat atria: an in vitro study

Scorpion envenomation is considered public health problem in Northern African countries. The mechanisms of cardiac dysfunction following scorpion envenomation are not fully understood. This study examined the effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide (ANP) release from rat atrium using in vitro organ perifusion. Male Sprague Dawley rats were used in this study. Three experiments were conducted. In experiment 1, atrial tissues were exposed either to Krebs-bicarbonate buffer medium (control) or to scorpion toxin (10(-8) M to 10(-6) M). In experiment 2, animals were chemically sympathectomized with a single intraperitoneal injection of 6-hydroxydopamine (6-OHDOPA) at a dose of 40 microg/g 24 h before sacrifice. Vehicle-treated rats served as control. Atrial tissues were collected and perifused in the presence of 10(-6) M scorpion toxin. In experiment 3, atrial tissues were exposed to 10(-6) M scorpion toxin either in the absence or presence of 10(-6) M propranolol (a beta-adrenoceptor blocker), or 10(-6) M tetrodotoxin (a sodium channel blocker). ANP levels released in the perifusion medium were determined by radioimmunoassay. The scorpion toxin at 10(-6) M induced a significant (p<0.01) increase (106%) in ANP levels. This effect was decreased (20%) by 6-OHDOPA. Propranolol and tetrodotoxin significantly (p<0.01) inhibited 55% and 60%, respectively, the toxin-induced ANP release. The data show that the North African scorpion toxin from Androctonus australis garzonii increases the ANP release in rat atrium through stimulation of sympathetic cardiac nerves and sodium channels activation.     

Characters in the book lungs of Scorpiones (Chelicerata,Arachnida) revealed by scanning electron microscopy

The fine structure of the book lungs in 29 species representing ten monophyletic taxa of the Scorpiones (Arachnida) was investigated using scanning electron microscopy (SEM). Scorpion lungs are not homogeneous across the group. Here we describe and score three sets of phylogenetically informative characters: (1) the surface ornament of the lung lamellae, (2) the distal margins of the lamellae and (3) the fine structure of the spiracle margin. Provisional results suggest that reticulation on the surface of the lung lamellae is characteristic of the Buthidae. By contrast, non-buthid scorpions maintain the air space between adjacent lamellae using projecting trabeculae. Typically they are simple struts, but the trabeculae are distally branched in all investigated Scorpionidae, plus at least one species belonging to the Liochelidae. Simple thorns on the lamellar margins probably represent the plesiomorphic condition, while more complex, branched, arcuate morphologies appear to be homoplastic, occurring sporadically in numerous scorpion sub-groups. The tightly packed, hexagonal pillars around the posterior margin of the spiracle support a close relationship between Scorpionidae and Liochelidae, to the exclusion of the Urodacidae.     

Gill microcirculation of the air-breathing climbing perch, Anabas testudineus (Bloch):relationships with the accessory respiratory organs and systemic circulation

The general macrocirculation and branchial microcirculation of the air-breathing climbing perch, Anabas testudineus, was examined by light and scanning electron microscopy of vascular corrosion replicas. The ventral aorta arises from the heart as a short vessel that immediately bifurcates into a dorsal and a ventral branch. The ventral branch distributes blood to gill arches 1 and 2, the dorsal branch to arches 3 and 4. The vascular organization of arches 1 and 2 is similar to that described for aquatic breathing teleosts. The respiratory lamellae are well developed but lack a continuous inner marginal channel. The filaments contain an extensive nutritive and interlamellar network; the latter traverses the filament between, but in register with, the inner lamellar margins. Numerous small, tortuous vessels arise from the efferent filamental and branchial arteries and anastomose with each other to form the nutrient supply for the filament, adductor muscles, and arch supportive tissues. The efferent branchial arteries of arches 1 and 2 supply the accessory air-breathing organs. Arches 3 and 4 are modified to serve primarily as large-bore shunts between the dorsal branch of the ventral aorta and the dorsal aorta. In many filaments from arches 3 and 4, the respiratory lamellae are condensed and have only 1-3 large channels. In some instances in arch 4, shunt vessels arise from the afferent branchial artery and connect directly with the efferent filamental artery. The filamental nutrient and interlamellar systems are poorly developed or absent. The respiratory and systemic pathways in Anabas are arranged in parallel. Blood flows from the ventral branch of the ventral aorta, through gill arches 1 and 2, into the accessory respiratory organs, and then returns to the heart. Blood, after entering the dorsal branch of the ventral aorta, passes through gill arches 3 and 4 and proceeds to the systemic circulation. This arrangement optimizes oxygen delivery to the tissues and minimizes intravascular pressure in the branchial and air-breathing organs. The efficiency of this system is limited by the mixing of respiratory and systemic venous blood at the heart.     

Heart inflow tract of the African lungfish Protopterus dolloi

We report a morphologic study of the heart inflow tract of the African lungfish Protopterus dolloi. Attention was paid to the atrium, the sinus venosus, the pulmonary vein, and the atrioventricular (AV) plug, and to the relationships between all these structures. The atrium is divided caudally into two lobes, has a common part above the sinus venosus, and appears attached to the dorsal wall of the ventricle and outflow tract through connective tissue covered by the visceral pericardium. The pulmonary vein enters the sinus venosus and runs longitudinally toward the AV plug. Then it fuses with the pulmonalis fold and disappears as an anatomic entity. However, the oxygenated blood is directly conveyed into the left atrium by the formation of a pulmonary channel. This channel is formed cranially by the pulmonalis fold, ventrally by the AV plug, and caudally and dorsally by the atrial wall. The pulmonalis fold appears as a wide membranous fold which arises from the left side of the AV plug and extends dorsally to form the roof of the pulmonary channel. The pulmonalis fold also forms the right side of the pulmonary channel and sequesters the upper left corner of the sinus venosus from the main circulatory return. The AV plug is a large structure, firmly attached to the ventricular septum, which contains a hyaline cartilaginous core surrounded by connective tissue. The atrium is partially divided into two chambers by the presence of numerous pectinate muscles extended between the dorsal wall of the atrium and the roof of the pulmonary channel. Thus, partial atrial division is both internal and external, precluding the more complete division seen in amphibians. The present report, our own unpublished observations on other Protopterus, and a survey of the literature indicate that not only the Protopterus, but also other lungfish share many morphologic traits.     

Characterizing left atrial appendage functions in sinus rhythm and atrial fibrillation using computational models

Clinical studies show that the left atrial appendage, a blind-ended structure that is attached to the left atrium, may be the cause of 90% of atrial thrombi in atrial fibrillation (abnormal heart rhythm), and it is much reduced in sinus (normal) rhythm. In this paper, the effects of blood flows in left atrium and left atrial appendage are studied to help characterize the atrial appendage functions in sinus rhythm and atrial fibrillation using mathematical models. Our results show that the left atrial appendage is not functional in sinus rhythm because the atrial transmitral velocities remained almost identical for atria with and without appendage, which agrees with the current clinical observations. However, in atrial fibrillation, a proper atrial contraction is absent, which causes the second emptying velocity (A-wave) to be missing in both transmitral velocity and appendage filling/emptying velocity. Without the proper emptying of the blood, vortices generated in the chamber remain high strengths and with longer durations. They induce ineffective emptying of the blood in the atrium and appendage, which then lead to blood stagnation and subsequent thrombus formation.     

Book lung development in juveniles and adults of the cobweb spider, Parasteatoda tepidariorum C. L. Koch, 1841 (Araneomorphae,Theridiidae)

Light and transmission electron microscopy were used to study the development of new book lung lamellae in juvenile and adult spiders (Parasteatoda tepidariorum). As hypothesized earlier in a study of embryos, mesenchyme cells dispersed throughout the opisthosoma (EMT) are a likely source of precursor epithelial cells (MET) for the new lamellae. The precursor cells in juveniles and adults continue many of the complex activities observed in embryos, e.g., migration, alignment, lumen formation, thinning, elongation, and secretion of the cuticle of air channel walls and trabeculae. The apicobasal polarity of precursor cells for new channels is apparently induced by the polarity pattern of precursor cells of channels produced earlier. Thus, new air and hemolymph channels extend and continue the alternating pattern of older channels. At sites more distant from the spiracle and atrium, new channels are usually produced by the mode II process (intracellular alignment and merging of vesicles). These air channels have bridging trabeculae and are quite stable in size throughout their length. At sites closer to the spiracle and atrium, new channels may be produced by mode I (coalescence of merocrine vesicle secretion). This raises the hypothesis that structural and functional differences in mode I and II channels and differing oxygen and fluid conditions with distance from the spiracle and atrium determine the mode of formation of new channels. Observations herein support an earlier hypothesis that there is some intercellular apical/apical and basal/basal affinity among the opposed surfaces of aligned precursor cells. This results in the alternating pattern of air channels at the apical and hemolymph channels at the basal cell surfaces.     

Myoanatomy and serotonergic nervous system of the ctenostome Hislopia malayensis: evolutionary trends in bodyplan patterning of ectoprocta

Background

Near the end of the nineteenth century the hypothesis was presented for the homology of book lungs in arachnids and book gills in the horseshoe crab. Early studies with the light microscope showed that book gill lamellae are formed by outgrowth and possibly some invagination (infolding) of hypodermis (epithelium) from the posterior surface of opisthosomal limb buds. Scorpion book lungs are formed near the bilateral sites of earlier limb buds. Hypodermal invaginations in the ventral opisthosoma result in spiracles and sac-like cavities (atria). In early histological sections of embryo book lungs, widening of the atrial entrance of some lamellae (air channels, air sacs, saccules) was interpreted as an indication of invagination as hypothesized for book gill lamellae. The hypodermal infolding was thought to produce the many rows of lamellar precursor cells anterior to the atrium. The ultrastructure of scorpion book lung development is compared herein with earlier investigations of book gill formation.

Results

In scorpion embryos, there is ingression (inward migration) of atrial hypodermal cells rather than invagination or infolding of the atrial hypodermal layer. The ingressing cells proliferate and align in rows anterior to the atrium. Their apical-basal polarity results in primordial air channels among double rows of cells. The cuticular walls of the air channels are produced by secretion from the apical surfaces of the aligned cells. Since the precursor cells are in rows, their secreted product is also in rows (i.e., primordial air channels, saccules). For each double row of cells, their opposed basal surfaces are gradually separated by a hemolymph channel of increasing width.

Conclusions

The results from this and earlier studies show there are differences and similarities in the formation of book lung and book gill lamellae. The homology hypothesis for these respiratory organs is thus supported or not supported depending on which developmental features are emphasized. For both organs, when the epithelial cells are in position, their apical-basal polarity results in alternate page-like channels of hemolymph and air or water with outward directed hemolymph saccules for book gills and inward directed air saccules for book lungs.     

Capsaicin-sensitive neural pathway mediates atrial natriuretic factor (ANF) release in response to physiological stimuli

Increases in intravascular volume are detected by mechanoreceptors situated at the junctions of the great veins with the atria. We had previously shown that localized distension of the superior vena caval/right atrial junction, simulating increased cardiac preload, elicits release of ANF remotely from the atrial appendage. We proposed that ANF secretion is stimulated via intrinsic neural pathways running from the venoatrial junctions to the appendage. We developed a technique whereby non-adrenergic, non-cholinergic sensory nerves could be selectively destroyed in the heart of adult rats by instilling capsaicin into the pericardial space. Four days later, the animals were killed, and isolated perfused atria were prepared with small balloons positioned so that the superior vena caval/right atrial junction could be discretely stretched. Immunoreactive ANF secretion into the perfusate was measured. Although distension of the venoatrial junction increased ANF secretion from the control atria, there was no such response in the denervated atria. We conclude (A) that local application of capsaicin to the heart of adult rats induces selective functional neural deficits and (B) that information regarding distension of the junction of the great veins and the atria is normally transmitted across the atrium via these nerves to stimulate ANF secretion from peptide stores located in the atrial appendage. We propose that these pathways are crucial to ensure appropriate ANF secretion in response to an increase in circulating blood volume.     

The ligament of Marshall as a parasympathetic conduit

The objective of the study was to investigate the morphology, distribution, and electrophysiological profile of the autonomic fibers that innervate the ligament of Marshall (LOM). Gross anatomical dissections were performed in 10 dogs. Sections of the left vagus nerve, left stellate ganglion, and the LOM were immunostained to identify adrenergic and cholinergic nerves. Hearts were also stained for acetylcholinesterase to identify epicardial cholinergic nerves. In vivo electrophysiological studies were performed in another 10 dogs before and after LOM ablation. The anatomical examination revealed that the LOM is innervated by a branch of the left vagus. Immunohistochemistry confirmed that these nerve bundles are predominantly cholinergic (cholinergic-to-adrenergic ratio of 12.6 +/- 3.9:1). Cholinergic nerves originating in the LOM were found to innervate surrounding left atrial structures, including the pulmonary veins, left atrial appendage, coronary sinus, and posterior left atrial fat pad. Ablation of the LOM significantly attenuated effective refractory period shortening at distant sites, such as pulmonary veins and left atrial appendage, in response to vagal stimulation (vagal-induced ERP decrease in the left atrium: baseline vs. postablation = 17 vs. 4%; P = 0.0056). In conclusion, the LOM contains a predominance of cholinergic nerve fibers. Cholinergic fibers arising from the LOM innervate surrounding structures and contribute to the electrophysiological profile of the left atrium. These findings may provide a basis for the role of the LOM in the genesis and maintenance of atrial fibrillation.     

Paracardioscopy provides endoscopic visualization of the heart

Paracardioscopy provides totally endoscopic access to the heart via a transabdominal, transdiaphragmatic approach. Structures such as the pulmonary veins, inferior vena cava, left and right atrial appendage, and posterior left atrium can be visualized. Epicardial cardiac procedures, such as ablation procedures for atrial fibrillation, can be successfully performed using this development. This report describes paracardioscopy.     

In vivo Observations on a Specialized Microvasculature,the Primary and Secondary Vessels in Fishes

Microscopical observations have been made on the blood circulation of intact, unanaesthetized specimens of the transparent glass catfish. Along the segmental arteries of the trunk, groups of short, curled vessels of capillary dimensions (termed inter-arterial anastomoses) branch off and reunite to form large so-called secondary arteries running parallel to the main (primary) arteries. Secondary arteries give rise to capillaries in the median ventral fin membrane. Secondary capilaries are drained via separate secondary veins. When blood passes from primary to secondary arteries via the inter-arterial anastomoses a pronounced plasma skimming is observed. Hence, blood perfusing the secondary capillaries of the fin membrane contains very few red blood cells.     

Fluid–structure interaction in a fully coupled three-dimensional mitral–atrium–pulmonary model

This paper aims to investigate detailed mechanical interactions between the pulmonary haemodynamics and left heart function in pathophysiological situations (e.g. atrial fibrillation and acute mitral regurgitation). This is achieved by developing a complex computational framework for a coupled pulmonary circulation, left atrium and mitral valve model. The left atrium and mitral valve are modelled with physiologically realistic three-dimensional geometries, fibre-reinforced hyperelastic materials and fluid–structure interaction, and the pulmonary vessels are modelled as one-dimensional network ended with structured trees, with specified vessel geometries and wall material properties. This new coupled model reveals some interesting results which could be of diagnostic values. For example, the wave propagation through the pulmonary vasculature can lead to different arrival times for the second systolic flow wave (S2 wave) among the pulmonary veins, forming vortex rings inside the left atrium. In the case of acute mitral regurgitation, the left atrium experiences an increased energy dissipation and pressure elevation. The pulmonary veins can experience increased wave intensities, reversal flow during systole and increased early-diastolic flow wave (D wave), which in turn causes an additional flow wave across the mitral valve (L wave), as well as a reversal flow at the left atrial appendage orifice. In the case of atrial fibrillation, we show that the loss of active contraction is associated with a slower flow inside the left atrial appendage and disappearances of the late-diastole atrial reversal wave (AR wave) and the first systolic wave (S1 wave) in pulmonary veins. The haemodynamic changes along the pulmonary vessel trees on different scales from microscopic vessels to the main pulmonary artery can all be captured in this model. The work promises a potential in quantifying disease progression and medical treatments of various pulmonary diseases such as the pulmonary hypertension due to a left heart dysfunction.

     

Effect of increased left atrial pressure on breathing frequency in anesthetized dog

Distension or loading of the isolated canine left heart caused reflex tachypnea in prior studies. The object of the present effort was to explore the possibility that this depended primarily on atrial distension. Cardiopulmonary bypass perfusion and ligation of pulmonary veins were used to isolate the left-heart chambers of anesthetized dogs. Simultaneous distension of the beating left atrium and fibrillating ventricle stimulated breathing frequency (f), whereas isolated ventricular distension did not. At other times, intervals of atrial fibrillation were imposed under two different conditions: 1) while the right heart and lungs were bypassed and systemic perfusion was provided by the left ventricle using blood returned to the left atrium by pump and 2) while the ventricles fibrillated and systemic perfusion was supplied directly by the pump. Atrial fibrillation increased left atrial pressure and stimulated f in condition 1. In condition 2, f increased only if fibrillation was associated with a rise in left atrial pressure. Vagal cooling blocked the effect of fibrillation. I conclude that left atrial distension may initiate reflex tachypnea.     

Cystid Structure and Protrusion of the Polypide in Crisia (Bryozoa, Cyclostomata)

The ultrastructure of the cystid of Crisia eburnea has been studied. The cystid wall comprises an outer periostracum, a calcified layer and one inner cell layer, the ectoderm. The membranous sac, which consists of an outer basement membrane, a series of very thin annular muscle cells and an inner layer of epithelial cells, is interpreted as the detached mesoderm of the cystid wall. Accordingly, the atrial sphincter and the generally eight branched, longitudinal muscle cells connecting the terminal membrane and the membranous sac are interpreted as ectoderm. The membranous sac is attached to the cystid wall with two lateral ligaments and at four abfrontal areas: 1) a wide distal area, 2) an area at the origin of the retractor muscles, 3) a small area between 1 and 2, and 4) a small basal area at the origin of a pair of small muscle cells attached to the lowermost part of the caecum.
We infer that the protrusion of the polypide is caused by a sequential contraction of the annular muscle cells of the membranous sac, starting basally and aided by the contraction of the longitudinal ectodermal muscle cells.     

Functional morphology of the heart and of a new cephalic pulsatile organ in the blowfly Calliphora vicina (Diptera: Calliphoridae) and their roles in hemolymph transport and tracheal ventilation

In the blowfly Calliphora vicina (Diptera: Calliphoridae), the morphology of the dorsal vessel and of a new cephalic accessory pulsatile organ (CPO) were analysed with light-microscopic, SEM and TEM techniques. The CPO and neck aorta are reconstructed 3-dimensionally by computer-aided design. The pulse activity of the CPO and of the heart was measured in intact flies over periods of several hours or days using contact-thermography with laser beam heat-marking. The intratracheal pressure was simultaneously measured at the anterior thoracic spiracle. The dorsal vessel is constructed of pairs of left–right alternating cells. Its enlarged chamber in the anterior abdomen contains two pairs of incurrent ostia, its posterior narrower heart tube possesses three pairs of incurrent ostia and paired caudal excurrent openings. The aorta opens with a funnel-like opening in the neck. Proportions, arrangement and ultrastructure of the aorta, heart cells and pericardial muscles are described. Cushionlike sarcoplasmic protrusions of heart cells (pair no. 17) probably function as internal valves. The neck aorta is constructed of a cuticular ‘roof’ deviating from the dorsal neck membrane and a ventral longitudinal muscle ‘floor’. The aorta is not kept open because of missing muscle or connective tissue strands. The underside of the CPO is fused with air sacs that function as antagonists to the muscles. The heart reverses its beat periodically in resting and active flies. During the longer forward-pulse periods, mean frequency is lower (about 3.0 Hz at Ta 20°C), during the shorter backward periods mean frequency is higher (4.6 Hz). The CPO beats only during forward-pulse periods of the heart with an independent and slower pulse rate (1.8 Hz). The CPO-pulses produce positive pressure pulses at the anterior thoracic spiracle. During backward-pulse periods of the heart and pulse pause of the CPO, a continuous negative pressure arises at the thoracic spiracle instead of pressure pulses. The intimate connection of an accessory pulsatile organ with tracheal air sacs makes it work as a bifunctional pump for hemolymph distribution and tracheal ventilation. Neurosecretory and synapsing innervation of the CPO in connection with aorta, heart and pericardial septum muscle innervation suggest that both organs are regulated and that the duration of their periods is neuronally coordinated.