Ontogeny of body density and the swimbladder in yellowtail kingfish Seriola lalandi larvae

The ontogeny of larval body density and the morphological and histological events during swimbladder development were investigated in two cohorts of yellowtail kingfish Seriola lalandi larvae to understand the relationship between larval morphology and body density. Larvae <3 days post hatch (dph) were positively buoyant with a mean ± s.d . body density of 1·023 ± 0·001 g cm^?3. Histological evidence demonstrated that S. lalandi larvae are initially transient physostomes with the primordial swimbladder derived from the evagination of the gut ventral to the notochord and seen at 2 dph. A pneumatic duct connected the swimbladder to the oesophagus, but degenerated after 5 dph. Initial swimbladder (SB) inflation occurred on 3 dph, and the inflation window was 3–5 dph when the pneumatic duct was still connected to the gut. The swimbladder volume increased with larval age and the epithelial lining on the swimbladder became flattened squamous cells after initial inflation. Seriola lalandi developed into a physoclist with the formation of the rete mirabile and the gas‐secreting gland comprised low‐columnar epithelial cells. Larvae with successfully inflated swimbladders remained positively buoyant, whereas larvae without SB inflation became negatively buoyant and their body density gradually reached 1·030 ± 0·001 g cm^?3 by 10 dph. Diel density changes were observed after 5 dph, owing to day time deflation and night‐time inflation of the swimbladder. These results show that SB inflation has a direct effect on body density in larval S. lalandi and environmental factors should be further investigated to enhance the rate of SB inflation to prevent the sinking death syndrome in the early life stage of the fish larvae.     

Development and function of the swimbladder-inner ear-lateral line system in the Atlantic menhaden,Brevoortia tyrannus (Latrobe)*

The swimbladder-acoustico-lateralis system of the Atlantic menhaden, Brevoortia tyrannus, is described and compared with that of the Atlantic herring, Clupea harengus. The system develops in the larva at a much earlier stage than the herring, being functional by about 2 mm tl. The volume of the gas-filled pro-otic bullae is five times that of the herring, and the gas ducts to the swimbladder, instead of being short and separate, are three times the length and join to form a common duct well in front of the swimbladder. The menhaden swimbladder is baggy and totally compliant when subjected to pressure changes. There is no toughened anterior end as in the herring, but the swimbladder is steeply angled in the body cavity, causing gas to collect at the anterior end after a pressure increase, unless the fish is diving very steeply. The guanine content of the swimbladder is comparable with that of the herring and makes the wall very impervious to gas diffusion. When subjected to quick pressure increases and decreases, the pro-otic membrane returns to its flat position with a time constant of 31-44 s. Very large quick pressure changes of about 3 atm burst the pro-otic membrane in adult fish but not in larvae.     

Morphological features of an endangered Japanese strain of Cyprinus carpio: reconstruction based on seven SNP markers

Morphological analyses of 183 specimens of Japanese common carp Cyprinus carpio (171 from Lake Biwa and 12 from nursery ponds) using genetic hybrid indices demonstrated that the typical native Japanese strain of C. carpio has a more elongate body, more branched dorsal‐fin rays, fewer and shorter gill rakers, more developed pneumatic bulb, more coiled pneumatic duct, longer posterior swimbladder and shorter intestine than the typical introduced C. carpio. These results provide a basis for a better understanding of the ecological characteristics and taxonomic status of the endangered Japanese strain of C. carpio.     

Limits of gas secretion by the salting-out effect in the fish swimbladder rete

Summary The high dissolved gas tensions required for the secretion of gases into deep-sea fish swimbladders are thought to be produced in the rete mirabile by a countercurrent multiplication mechanism, the capacity of which is theoretically limited by the physical characteristics of the rete and by the magnitudes of minute gas solubility changes in the blood plasma. These gas solubility changes are presumably induced through the salting-out effect following the addition of lactic acid to rete venous blood as it circulates through the gas gland. In order to estimate the maximum swimbladder gas pressures attainable by this mechanism, the effects of lactic acid on N₂ and Ar solubilities in water were determined at 5 and 25°C with a new volumetric method. The results show that the salting-out effect with lactic acid is much smaller than with NaCl, and that the agreement between predicted and observed swimbladder gas pressures is more critically dependent on the physical properties of the rete vasculature than indicated by previous theoretical treatments. When augmented by the release of hemoglobin-bound O₂, the salting-out effect with lactic acid appears large enough to account for the production of even the highest swimbladder O₂ pressures, provided the rete characteristics lie within certain reasonable limits. However, successful theoretical explanation of observed swimbladder N₂ pressures in some deep-sea species will require rigorous attention to such theoretically neglected factors as dissolved gas backdiffusion along the rete and the unequal size and number of the rete arterial and venous capillaries.     

The occurrence and distribution of peptide- or 5-HT-containing nerves in the swimbladder of four different species of teleosts (Gadus morhua,Ctenolabrus rupestris,Anguilla anguilla,Salmo gairdneri)

Summary The innervation of the swimbladder in four different teleost species has been studied by the use of immunohistochemical methods. The teleosts examined belong to two different groups regarding their swimbladder morphology: physoclists (the cod, Gadus morhua and the goldsinny wrasse, Ctenolabrus rupestris) and physostomes (the eel, Anguilla anguilla and the rainbow trout, Salmo gairdneri). Vasoactive intestinal polypeptide-like immunoreactivity was demonstrated in nerves of the swimbladder walls of all four species, and in the gas glands of the cod and the goldsinny wrasse. Substance P-like immunoreactivity was shown in swimbladders of the cod, eel and rainbow trout but not the goldsinny wrasse. Immunoreactivity to met-enkephalin antiserum was revealed in the swimbladder walls of the eel and the goldsinny wrasse, while neurotensin-like immunoreactivity was present in the goldsinny wrasse and rainbow trout swimbladders. Neurotensin-like immunoreactivity was also seen in the gas gland of the goldsinny wrasse. 5-Hydroxytryptamine immunoreactivity was found in endocrine cells in the pneumatic duct of the eel and in the swimbladder walls of the goldsinny wrasse and the rainbow trout. In conclusion, all teleosts examined showed a very close resemblance in the peptidergic/tryptaminergic innervation of the swimbladder to that of the gut, inasmuch as the immunoreactivity present in the swimbladders always occurred in the gut of the same species.     

The ultrastructure of the swimbladder of the toadfish,Opsanus tau L.

Summary The anterior chamber of the swimbladder of the toadfish Opsanus tau L. is lined by a single layer of columnar gas gland cells, cuboidal cells that resemble gas gland cells but are located outside of the gas gland region, and squamous cells. Multilamellar bodies are numerous in the gas gland cells and the cuboidal cells and are present in smaller numbers in the squamous cells. Capillaries lie in the lamina propria directly below the epithelial lining. A thick continuous muscularis mucosae and a submucosa consisting of tightly packed cells, cell processes, and connective tissue may contribute to the impermeability to gases of the wall of the anterior chamber.The posterior chamber of the swimbladder is lined by a single type of squamous epithelial cell. Multilamellar bodies were occasionally observed in these cells also. Other types of cells frequently form a partial second layer between the epithelial lining and the basement lamina. A thin muscularis mucosae lies directly below the basement lamina and the capillaries of the posterior chamber are located in the submucosa. The tunica externa is a layer of dense connective tissue that surrounds both the anterior and posterior chambers. Collagen fibrils in the form of tactoids are present in this layer.Part of this work was submitted by S.M.M. in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Biology Department, Boston University. S.M.M. is grateful for a National Science Foundation Traineeship.     

Development of the swimbladder and its innervation in the zebrafish, Danio rerio

Many teleosts including zebrafish, Danio rerio, actively regulate buoyancy with a gas-filled swimbladder, the volume of which is controlled by autonomic reflexes acting on vascular, muscular, and secretory effectors. In this study, we investigated the morphological development of the zebrafish swimbladder together with its effectors and innervation. The swimbladder first formed as a single chamber, which inflated at 1-3 days posthatching (dph), 3.5-4 mm body length. Lateral nerves were already present as demonstrated by the antibody zn-12, and blood vessels had formed in parallel on the cranial aspect to supply blood to anastomotic capillary loops as demonstrated by Tie-2 antibody staining. Neuropeptide Y-(NPY-) like immunoreactive (LIR) fibers appeared early in the single-chambered stage, and vasoactive intestinal polypeptide (VIP)-LIR fibers and cell bodies developed by 10 dph (5 mm). By 18 dph (6 mm), the anterior chamber formed by evagination from the cranial end of the original chamber; both chambers then enlarged with the ductus communicans forming a constriction between them. The parallel blood vessels developed into an arteriovenous rete on the cranial aspect of the posterior chamber and this region was innervated by zn-12-reactive fibers. Tyrosine hydroxylase- (TH-), NPY-, and VIP-LIR fibers also innervated this area and the lateral posterior chamber. Innervation of the early anterior chamber was also demonstrated by VIP-LIR fibers. By 25-30 dph (8-9 mm), a band of smooth muscle formed in the lateral wall of the posterior chamber. Although gas in the swimbladder increased buoyancy of young larvae just after first inflation, our results suggest that active control of the swimbladder may not occur until after the formation of the two chambers and subsequent development and maturation of vasculature, musculature and innervation of these structures at about 28-30 dph.     

A finite interval of initial swimbladder inflation in Latris lineata revealed by sequential removal of water‐surface films

A finite interval of initial swimbladder inflation in striped trumpeter Latris lineata larvae occurred over 4 days at 16° C. Water‐surface films were removed on different days to form treatments: 4, 8, 9, 10, 11 and 12 days post hatching, dph (day 4, 8, 9, 10, 11 and 12 treatments, respectively). No swimbladder inflation was recorded prior to water‐surface film removal. When the water‐surface films were removed in day 4 and 8 treatments, initial swimbladder inflation was first recorded in larvae 9 dph at mean ± s .e . 35·0 ± 5·4%(n = 4) and 45·0 ± 7·9%, respectively. Water‐surface film removal at days 9, 10 and 11, resulted in initial swimbladder inflation the following day at 62·5 ± 2·5, 62·5 ± 7·2 and 11·3 ± 5·5% in larvae 10, 11 and 12 dph, respectively. No swimbladder inflation was recorded following water‐surface film removal on day 12. There was no significant difference in initial inflation among larvae in day 4, 8, 9 and 10 treatments, ranging from 65·0 ± 4·1 to 73·8 ± 6·9%(P > 0·05). Initial inflation was significantly lower in the day 11 treatment (11·3 ± 5·5%)(P < 0·05). During the inflation interval (9–12 dph) swimbladders displayed one of three morphologies; liquid dilation, gas inflated and collapsed. Collapse of the swimbladder lumen was first apparent in larvae without swimbladder inflation from 11 dph and progressively developed thereafter in all larvae with non‐inflated swimbladders. Larvae >6·1 mm standard length lost the ability to undergo initial swimbladder inflation. This study demonstrates that the interval for initial swimbladder inflation in striped trumpeter is short, finite and related to larval size. The end of the inflation interval was marked by onset of abnormal swimbladder morphologies, but not to closure of the pneumatic duct.     

Cytochemical study of the lamellar bodies in the swimbladder of the toadfish Opsanus tau L.

Summary The columnar epithelial cells of the gas gland in the swimbladder of the toadfish, Opsanus tau L., contain lamellar bodies that resemble the lamellar bodies found in epithelial cells of vertebrate lungs. Cytochemical assays indicate that swimbladder lamellar bodies are soluble in chloroform-methanol solution, react with tricomplex flocculation solution (indicating a phospholipid component), exhibit a positive reaction for cholesterol when exposed to digitonin, and contain acid phosphatase.The anterior chamber of the toadfish swimbladder is lined by an extracellular layer. Digitonin-cholesterol crystals are found in this layer when the swimbladder is treated with digitonin. A ruthenium red positive layer is also present in the anterior chamber of the toadfish swimbladder.The structure and cytochemistry of swimbladder lamellar bodies are compared with those of vertebrate lung lamellar bodies. Similarities between the extracellular layer in the swimbladder and the extracellular layer in lungs are also noted.Supported in part by a grant No 1 R23 HL 19593-01 from the National Institutes of Health     

Sound production by a recoiling system in the pempheridae and terapontidae

Sound‐producing mechanisms in fishes are extraordinarily diversified. We report here original mechanisms of three species from two families: the pempherid Pempheris oualensis, and the terapontids Terapon jarbua and Pelates quadrilineatus. All sonic mechanisms are built on the same structures. The rostral part of the swimbladder is connected to a pair of large sonic muscles from the head whereas the posterior part is fused with bony widenings of vertebral bodies. Two bladder regions are separated by a stretchable fenestra that allows forward extension of the anterior bladder during muscle contraction. A recoiling apparatus runs between the inner face of the anterior swimbladder and a vertebral body expansion. The elastic nature of the recoiling apparatus supports its role in helping the swimbladder to recover its initial position during sonic muscle relaxation. This system should aid fast contraction (between 100 and 250Hz) of sonic muscles. There are many differences between species in terms of the swimbladder and its attachments to the vertebral column, muscle origins, and morphology of the recoiling apparatus. The recoiling apparatus found in the phylogenetically‐related families (Glaucosomatidae, Pempheridae, Terapontidae) could indicate a new character within the Percomorpharia. J. Morphol. 277:717–724, 2016. © 2016 Wiley Periodicals, Inc.     

The homologies of the lorisoid internal carotid artery system

The development of the “internal carotid” arterial system of the lesser galago (Galago senegalensis senegalensis)is described. The first artery to be formed is a typical promontory artery which runs through the middle-ear cavity and gives off the stapedial artery. It terminates in the cranial cavity by dividing into the middle cerebral, anterior cerebral, and two ophthalmic arteries. It is accompanied by the internal carotid nerve. A medially directed artery to the external carotid rete arises from the commencement of the promontory artery and joins the caudal end of the rete, whose cranial end lies in the foramen lacerum. As the promontory artery enters the cranial cavity, it communicates with the cranial end of the rete. The promontory artery, between the origin of the artery to the rete and its connection with the rete, becomes narrowed and eventually disappears. Thus the internal carotid artery is formed from the commencement of the promontory artery, the artery to the rete, the external carotid rete, and the terminal intracranial part of the promontory artery. The relationships of the artery to the rete indicate that it is the homologue of the human ascending pharyngeal artery.     

Expression and function of mouse Sox17 gene in the specification of gallbladder/bile-duct progenitors during early foregut morphogenesis

In early-organogenesis-stage mouse embryos, the posteroventral foregut endoderm adjacent to the heart tube gives rise to liver, ventral pancreas and gallbladder. Hepatic and pancreatic primordia become specified in the posterior segment of the ventral foregut endoderm at early somite stages. The mechanisms for demarcating gallbladder and bile duct primordium, however, are poorly understood. Here, we demonstrate that the gallbladder and bile duct progenitors are specified in the paired lateral endoderm domains outside the heart field at almost the same timing as hepatic and pancreatic induction. In the anterior definitive endoderm, Sox17 reactivation occurs in a certain population within the most lateral domains posterolateral to the anterior intestinal portal (AIP) lip on both the left and right sides. During foregut formation, the paired Sox17-positive domains expand ventromedially to merge in the midline of the AIP lip and become localized between the liver and pancreatic primordia. In Sox17-null embryos, these lateral domains are missing, resulting in a complete loss of the gallbladder/bile-duct structure. Chimera analyses revealed that Sox17-null endoderm cells in the posteroventral foregut do not display any gallbladder/bile-duct molecular characters. Our findings show that Sox17 functions cell-autonomously to specify gallbladder/bile-duct in the mouse embryo.     

Development of the swimbladder in the European eel (Anguilla anguilla)

The swimbladder of the adult eel, Anguilla anguilla, with its bipolar countercurrent system, the rete mirabile, is a widely used model for swimbladder function, but very little is known about the development of this swimbladder. Our histological studies on the developing swimbladder revealed that during metamorphosis the swimbladder becomes present as a dorsal outgrowth of the esophagus. It is filled with surfactant, and gas was not detected in the swimbladder. In the young glass-eel, the epithelial (gas gland) cells of the swimbladder are columnar, but do not yet have the typical basolateral labyrinth established in adult animals. Few blood vessels are found in the swimbladder tissue, and the submucosa is present as a thick layer of connective tissue, giving a large diffusion distance between blood vessel and swimbladder lumen. Within the next 2 or 3 months of development, gas gland cells develop their typical basolateral labyrinth, and the thickness of the submucosa is significantly reduced, resulting in a short diffusion distance between blood vessels and the swimbladder lumen. The first filling of the swimbladder with gas is observed while the gas gland cells are still in a poorly differentiated status and it appears unlikely that these cells can accomplish their typical role in gas deposition. The presence of small gas bubbles in the swimbladder as well as in the ductus pneumaticus at the time of initial swimbladder inflation suggests that the swimbladder is filled by air gulping or possibly by taking up gas bubbles from the water.     

Morphological development of the swim bladder in hatchery-reared striped trumpeter Latris lineata

This study examined swim bladder morphogenesis in three cohorts of striped trumpeter (Latris lineata), a euphysoclist species with physostomous larvae. The swim bladder was first discernible 1–2 days after hatching as an evagination on the dorsal surface of the incipient digestive tract. It comprised a cluster of mesenchymal cells surrounding an inner primordium of epithelial cells. At mouth opening in larvae of 5.3 mm standard length (SL), the swim bladder was noticeably enlarged. Histologically, the swim bladder lumen was dilated and liquid filled. The pneumatic duct was first seen during the dilation stage and the rete mirabile began forming among the connective tissue surrounding the swim bladder. Initial swim bladder inflation occurred on day 11 post‐hatching in Cohort 1, at 14°C, and day 9 post‐hatching, in Cohorts 2 and 3, at 16°C. Histologically, the lumens of inflated swim bladders were ellipsoid and the epithelium was squamous, except for cuboidal gas gland cells at the anterio‐ventral and anterio‐lateral regions of the swim bladder. During the initial inflation interval the pneumatic duct was dilated in larvae both with and without swim bladder inflation. The pneumatic duct began to regress in some larvae over 7.5 mm SL. The swim bladder of striped trumpeter was similar to larvae of other altricial perciform marine fish in respect to organ derivation, tissue differentiation, luminal dilation and initial gaseous inflation. However, variations, particularly the delay in initial swim bladder inflation until after the start of feeding, were observed that could be fundamental to problems encountered during larval rearing.     

A new genus, Leptomelanosoma, for the polynemid fish previously known as Polydactylus indicus (Shaw, 1804) and a redescription of the species

A new genus, Leptomelanosoma, is proposed for the polynemid fish, Polydactylus indicus (Shaw, 1804). The genus differs from all other genera in the family Polynemidae by the following combination of characters: anterior one-third of lower jaw with small teeth extending onto lateral surface, adjacent portion of lip poorly developed; ethmoid not covered dorsally by frontals; sphenotics visible dorsally between anterior margins of parietal and pterotic; upper and lower caudal fin lobes very long, filamentous; swimbladder with many appendages inserted into lateral walls of abdominal cavity; grayish-black body. The type species, Polydactylus indicus, is redescribed as Leptomelanosoma indicum. Received: September 19, 1999 / Revised: June 9, 2000 / Accepted: July 10, 2000     

O2-filled swimbladder employs monocarboxylate transporters for the generation of O2 by lactate-induced root effect hemoglobin

The swimbladder volume is regulated by O(2) transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the "Root effect." While O(2) generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H(+)/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.     

Uptake of3H-adrenaline and14C-noradrenaline into neuronal and extraneuronal tissue compartments in the perfused gas gland of the swimbladder of the Atlantic cod,Gadus morhua

Summary The neuronal and extraneuronal accumulation of radiolabelledl-adrenaline andl-noradrenaline was studied in the gas gland of the swimbladder of the Atlantic cod,Gadus morhua. Both amines are taken up into the tissue compartments, and a preference for noradrenaline for both uptake processes was demonstrated. A relatively high neuronal accumulation compared to earlier results (cod spleen; Ungell and Nilsson 1984) was seen and this is probably due to the more dense innervation of the swimbladder gas gland. A higher extraneuronal accumulation may be due to the presence of arterial smooth muscle.It is concluded that the adrenergic nerves of the swimbladder gas gland of the cod preferentially accumulate noradrenaline, a situation similar to that in mammals.Abbreviations A/NA adrenaline/noradrenaline ratio - PBA phenoxybenzamine - PNMT phenylethanolamine-N-methyl tranferase     

Salivary glands in Cicadidae (Hemiptera: Cicadoidea): comparative morphology, ultrastructure, and their phylogenetic significance

The present investigation provides information on gross morphology and ultrastructure of salivary glands of species in Cicadidae in detail. The structure of the salivary glands of 11 representative species from 10 genera belonging to three subfamilies of Cicadidae was studied using light microscopy and transmission electron microscopy. In the examined species, the salivary glands are paired structures, and each of which is comprised of a principal gland (pg) and an accessory gland (ag). The pg is divided into anterior and posterior lobes, and both of which consist of numerous long digitate lobules. The lobules at the base of the long digitate lobules of posterior lobe are greatly short; here, we named as “short lobules.” All the lobules vary in size, disposition, length, and shape. The anterior lobe and posterior lobes are connected by an anterior–posterior duct (apd). Two efferent salivary ducts (esd), derived from corresponding posterior lobes, fuse to form a short common duct which enters into the saliva syringe. The ag is composed of a greatly tortuous and folded accessory salivary tube, a gular gland (gg) constituting of several acini, and an accessory salivary duct (asd). The asd joins the esd at the place where the latter emergences. Constituents and arrangement of the salivary glands, the number and shape of the long digitate lobules in the anterior and posterior lobes, and the visibility of the apd were promising characters for the taxonomic and phylogenetic analysis of Cicadoidea. The variations of secretory granules in size, shape, and electron density in lobule cells of pg of Platypleura kaempferi probably indicating different materials are synthesized. The absence of the infoldings of basal plasma membrane in the basal area of the cells and the presence of electron-lucent vesicles in the cytoplasm of the gg cells of P. kaempferi might suggest that the secretions of gg are more watery.     

Swimbladder and skeletal deformations in hatchery bred Spams aurata

Among hatchery bred Sparus aurata , 5.4% of the offspring of a single parent pair showed severe skeletal deformations coupled with marked growth retardation and pathological changes in the swimbladder. This resulted from extreme proliferation, then hypertrophy, of the cuboidal epithelial cells of the gas gland and proliferation of the rete mirabile. This caused almost complete congestion of the swimbladder air space. The nature of the pathological changes in the swimbladder and the possibility of hereditary origin for both the skeletal and swimbladder deformations are discussed.     

SPERMIOGENESIS IN BARNACLES WITH SPECIAL REFERENCE TO ORGANIZATION OF THE ACCESSORY BODY*

Ultrastructural changes during spermiogenesis in the barnacles, Balanus amphitrite albicostatus, Balanus tintinnabulum rosa, Balanus trigonus and Tetraclita squamosa japonica, and organization of the sperm with special reference to the accessory body were studied. The Golgi complex organizes both the acrosome and the accessory body at different stages during spermiogenesis; the former is formed at the mid-spermatid stage and the latter is formed at the late spermatid stage. The arrangement of the components in the mature filiform sperm is quite unique, with the acrosome, the basal body just behind the acrosome, the axial filament parallel to a long nucleus, and a slender long mitochondrion behind the nucleus. The sperm in the anterior and posterior half of the ejaculatory duct differ from each other in form in that the sperm in the anterior duct are not equipped with the accessory body and the sperm in the posterior duct are. The accessory body can be artificially broken down by some treatments (1 M urea, alkaline sea water: pH 9.0-9.7, low ionic concentration of sea water). The loss of the accessory body from the sperm is assumed to be related to the ferti-lizability of the sperm.