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.     

Regulation of air and blood flow through the booklungs of the desert scorpion, Paruroctonus mesaensis

Injections of dye, latex and India ink were used to reveal the path of hemolymph circulation through the scorpion booklungs. Fine, branched arteries carry blood directly to muscle and other organs. The blood returns through venous channels to the ventral mesosoma where it passes laterally through the booklungs and into the pneumocardial veins just beneath the pleural cuticle. Blood flows dorsally through these veins to the pericardial sinus and heart. The scorpion has four pairs of booklungs located in the anterior segments of the ventral mesosoma. Each booklung has a spiracle which opens into an atrium enclosed by cuticular membrane. Air passes from the atrium into the booklung lamellae. Agitation of the animal or application of CO(2) causes retraction of the anterior and posterior atrial membrane. This expands the atrial chamber and allows gas exchange in the booklung lamellae. The posterior atrial membrane has a specialized region which forms a springy valve. This normally closes the spiracle unless pulled open by contraction of the attached poststigmaticus muscle. The pectens and receptors within the atrium may mediate the responses to CO(2). Slender hypocardial ligaments containing muscle fibers extend from the heart (dorsal mesosoma) to the booklungs in the ventral mesosoma. Heart movements thus cause dorso-ventral movement of the booklungs. The significance of these movements is as yet unclear. They may increase ventilation, help force blood to the heart and/or agitate the blood and booklung lamellae and thereby aid gas exchange. Passage of blood through the booklungs is regulated by dorsal and ventral muscles attached to the atrium at the lateral edge of the booklung. Contraction of the ventral atrial muscle closes the excurrent channel for passage of blood from the booklung into the pneumocardial vein. Electrical stimulation of the segmentai nerves from the subesophageal and first three abdominal ganglia causes spiracle opening and contraction of muscles attached to the atrial membrane. A previous study showed that these same segmental nerves also modulate heart activity. They thus provide a major pathway for regulation of the respiratory and circulatory systems.     

Embryonic development of the alimentary canal and ectodermal derivatives in the primitive moth,Neomicropteryx nipponensis issiki (Lepidoptera,Micropterygidae)

The formation of the alimentary canal, nervous system, and of other ectodermal derivatives in the embryo of the primitive moth, Neomicropteryx nipponensis Issiki, is described. The stomodaeum is formed from an invagination in the medioposterior portion of the protocephalon. The proctodaeum arises as an extension of the amnioproctodaeal cavity. The midgut epithelium orginates from anterior and posterior rudiments in blind ends of the stomodaeum and proctodaeum. The decondary dorsal organ is formed in developing midgut. The development of the brain is typical of insects. The ventral nerve cord originates in large part from neuroblasts arising in 3 gnathal, 3 thoracic, and 11 abdominal segments. Intrasegmental median cord cells probably differentiate into both ganglion cells and glial elements of the ventral nerve cord; intersegmental cells appear not to participate in the formation of the nervous system. The stomatogastric nervous system develops from three evaginations in the dorsal wall of the stomodaeum, and consists of the frontal, hypocerebral, and ventricular ganglia, the recurrent nerve, and corpora cardiaca. Five stemmata arise from the epidermis on each side of the head. Five pairs of ectodermal invaginations are formed in the cephalognathal region to produce the tentorium, mandibular apodemes, corpora allata, and silk glands. Prothoracic glands orginate in the prothorax. Mesothoracic spiracles shift anteriorly to the prothorax during development. Oenocytes arise in the first seven abdominal segments. Invaginated pleuropodia are formed in the first abdominal segment.     

The pronephros of the early ammocoete larva of lampreys (Cyclostomata,Petromyzontes): Fine structure of the renal tubules

Summary The renal tubules of the paired pronephros in early larvae (ammocoetes) of two lamprey species, Lampetra fluviatilis and Petromyzon marinus, were studied by use of light-, scanning- and transmission electron microscopy. They consist of (1) a variable number of pronephric tubules (3 to 6), and (2) an excretory duct. By fine-structural criteria, the renal tubules can be divided into 6 segments. Each pronephric tubule is divided into (1) the nephrostome and (2) the proximal tubule, the excretory duct consisting of (3) a common proximal tubule followed by (4) a short intermediate segment, and then by a pronephric duct composed of (5) a cranial and (6) a caudal section. The epithelium of the nephrostome displays bundles of cilia. The cells of the proximal tubule possess a brush border, many endocytotic organelles and a system of canaliculi (tubular invaginations of the basolateral plasmalemma). The same characteristics are encountered in the epithelium of the common proximal tubule; however, the number of these specific organelles decreases along the course of this segment in a posterior direction. In the intermediate segment, the epithelium appears structurally nonspecialized. The cells of the cranial pronephric duct lack a brush border; they have an extensive system of canaliculi and numerous mitochondria. The caudal pronephric duct is lined by an epithelium composed of light and dark cells; the latter are filled with mitochondria and the former contain mucus granules beneath the luminal plasmalemma. The tubular segments found in the pronephros are the same in structure and sequence as in the lamprey opisthonephroi. However, only the nephrostomes and proximal tubules occur serially in the pronephros, while the common proximal tubule, the intermediate segment and the cranial pronephric duct form portions of a single excretory duct.This paper is dedicated to the memory of Professor W. Bargmann, long-time editor of Cell and Tissue Research, the author of a splendid review on the structure of the vertebrate kidney and a master of German scientific writing.     

Morphology of the pronephros of the juvenile brown trout, Salmo trutta

The pronephros in juvenile brown trout (Salmo trutta) consists of a large ovoid renal corpuscle and a pair of tubules. The corpuscle is retained for 11 months, after which the glomerulus regresses. The glomerular arteries come directly from the dorsal aorta. The interstitium is permeated with venous blood vessels that arise from the anterior cardinal veins and are closely apposed to the tubules. Two distinct segments of the pronephric tubular system are distinguished by the histological and ultrastructural features of their component cells: 1) a short, transitional neck in which cells change from capsular epithelium to columnar epithelium, typical of tubules; 2) the convoluted segment composed of cells similar to first proximal tubular cells of the opisthonephros with well-formed brush borders, apical vesicles that vary in size and number along this segment, and lysosomes. Pinocytosis and exocytosis are also evident in this segment. The tubular system increases in length and in its convolutions until about week 9, when the opisthonephros develops. Distally each tubule connects with a Wolffian duct, with cells marked by the absence of apical inclusions and the presence of a uniform brush border, numerous mitochondria, and elaborate infolding of the basalar membrane. Nephrostomes, which are often characteristic of pronephroi, are not present. Cells with long cilia are found throughout the tubular system but are most characteristic of the neck and Wolffian-duct segments.     

Structure of ovaries in ensign scale insects,the most primitive representatives of Coccomorpha (Insecta,Hemiptera)

The ovaries of Orthezia urticae and Newsteadia floccosa are paired and composed of numerous short ovarioles. Each ovariole consists of an anterior trophic chamber and a posterior vitellarium that contains one developing oocyte. The trophic chamber contains large nurse cells (trophocytes) and arrested oocytes. The total number of germ cells per ovariole (i.e., cluster) is variable, but it is always higher than 32 and less than 64. This suggests that five successive mitotic cycles of a cystoblast plus additional divisions of individual cells are responsible for the generation of the cluster. Cells of the trophic chamber maintain contact with the oocyte via a relatively broad nutritive cord. The trophic chamber and oocyte are surrounded by somatic cells that constitute the inner epithelial sheath around the former and the follicular epithelium around the latter. Anagenesis of hemipteran ovarioles is discussed in relation to the findings presented. © 1995 Wiley-Liss, Inc.     

Organ culture of human seminiferous tubules: A useful tool to study the role of nerve growth factor in the testis

Summary Seminiferous tubules from human testes were mechanically isolated, the cut edges were sealed, and the tubules were cultured in medium free of fetal calf serum (FCS). Degeneration of germ cells occurred during the culture period and was paralleled by a disruption of the seminiferous epithelium, a disturbance in morphology and function of Sertoli cells, and a thickening of the lamina propria. However, when tubules were cultured for 5 days in the presence of FCS, degeneration of the spermatogenic tissue was reduced. FCS increased the mitotic activity of germ cells, but did not maintain normal morphology and function of Sertoli cells and cellular elements of the lamina propria. The thickening of the tubular wall concurred with a change in phenotype of lamina-propria cells from myoid to fibroblastic. Addition of nerve growth factor (NGF) to the culture medium (i) maintained the myoid phenotype of lamina-propria cells, (ii) prevented thickening of the tubular wall, and (iii) stabilized Sertoli cell morphology and function. The effects of NGF appeared to depend on the trophic effects of FCS, since NGF alone had no influence on the maintenance of a regular morphology of the spermatogenic epithelium. The present results indicate a decisive role for NGF in stabilizing specific functions of seminiferous tubules.     

Morphological and histochemical studies on oogenesis in Callosobruchus analis Fabr. (Bruchidae-Coleoptera)

The ovary in Callosobruchus analis consists of telotrophic ovarioles with the so called nurse cells confined to one chamber at the anterior end of the ovariole. There are three types of lipids in the ovary: (1) L₁ bodies that are present in the early oocytes, in the posterior prefollicular tissue and in the follicular epithelium and contain unsaturated phospholipids; (2) L₂ bodies that have a complete or incomplete sheath of phospholipids and a triglyceride core; (3) L₃ bodies that are formed of highly saturated triglycerides. Lipids are absent from the trophic tissue. In a mature oocyte the L₁ and L₂ bodies are cortical in distribution while the L₃ bodies are centrally located. The mitochondria contain lipoproteins with RNA. The yolk spheres are acid mucopolysaccharides and protein in nature. The precursors of the yolk spheres appear first in the cortical coplasm and are absent from the follicular epithelium or the trophic tissue. The nucleolus of the oocyte shows evidence of extrusions that are believed to pass into the ooplasm. There are no nutritive cords connecting the trophic tissue to the oocytes; nor is there any evidence of any histochemically demonstrable nutritive material being contributed to the oocyte by the trophic tissue. The circumstantial evidence points towards a contribution of the raw materials to the oocyte by the haemolymph either through or in between the follicular epithelium in some soluble form or as submicroscopic particles.     

Identification of stage-specific proteins synthesized by rat seminiferous tubules

Experiments were conducted to determine how the cycle of the seminiferous epithelium influenced synthesis and secretion of proteins by seminiferous tubules. Tubular segments were treated with collagenase and then cultured with [35S]methionine. These myoid cell-depleted tubules isolated from different stages of the epithelial cycle exhibited, at Stages VI and XII, two distinct peaks of secretion of total radiolabeled proteins. Two-dimensional gel electrophoresis indicated that the patterns of secreted proteins from these two stages were remarkably different, while those from other stages were intermediate between those at the peaks. At least 15 proteins were secreted cyclically, many of them previously unrecognized products of the seminiferous epithelium. One product, designated Cyclic Protein-2 (CP-2), exhibited a pronounced cycle of secretion, its peak at Stage VI being 30-fold greater than at its nadir at Stages XII-XIV. Further investigation indicated that CP-2 did not appear to originate from myoid cells or dispersed germ cells but could be recovered from Sertoli cell-enriched cultures prepared from Stage VI tubules. Protein secretion by tubular segments was also characterized by immunoprecipitation with two polyspecific antisera directed against Sertoli cell products. Five secretory proteins were identified which had cycles different from one another and from CP-2. In contrast to secreted products, the synthesis of most cellular proteins by tubular segments remained relatively constant throughout the cycle. It is concluded: 1) segments of the seminiferous epithelium secrete proteins into the culture medium which are distinct from cellular proteins; 2) the synthesis of many of these proteins varies with the epithelial cycle; and 3) several of the secreted proteins are of Sertoli cell origin, including a newly identified protein, CP-2. This indicates that the morphology and the protein synthetic capacity of the seminiferous epithelium are coordinated over space and time.     

Vitellogenesis in the milkweed bug,Oncopeltus fasciatus Dallas (Hemiptera). A light and electron microscopic investigation

Histochemical and electron microscopic methods have revealed that there are four types of cell inclusions in the late vitellogenic oocytes of Oncopeltus. (a) Type 1 is a vacuole which seems to be contributed from the tropharium via the nutritive tubes. It is suggested that this type consists partly at least of nucleolus-like material (ribonucleoprotein) emitted from the nuclei of the Zone III trophocytes. (b) Type 2 is lipid yolk which in early stage oocytes seems to be produced in the “Balbiani body.” In the vitellogenic oocytes these lipid spheres are apparently imported by the oocyte from the haemolymph either through the follicle cells, or through the extracellular space in the follicular epithelium. (c) Type 3 is carbohydrate/protein yolk where at least part of the protein (“vitellogenic protein”) is taken up from the haemolymph, transported through the extracellular space in the follicular epithelium, and deposited into the oocyte by pinocytosis. (d) Glycogen is deposited from the early phases of vitellogenesis. The tropharium may contribute, besides Type 1 vacuoles, ribosomes, mitochondria, stacks of annulated lamellae, and “food vacuoles” to the oocytes. Specialized cells which line the tropharium and send projections toward the trophic core have been called “peripheral trophocytes.” Contrary to the regular trophocytes, they contain glycogen and an abundance of Golgi complexes.     

Cell proliferation and rearrangement in the development of the Malpighian tubules of the hemipteran, Rhodnius prolixus

The pattern of cell activities resulting in the generation of a simple tubular epithelium, the Malpighian tubules of Rhodnius prolixus, is examined during embryogenesis. The anlage of the tubules is shown to be of ectodermal origin. An evolving pattern of cycling cells in the primordia is revealed using the immunocytochemical localization of a substituted nucleotide, BUdR. A cell unique to each tubule is shown not to enter the cell cycle but to be required for the proliferation of the remaining cells in the tubules. Furthermore, the activity of this cell imposes on each tubule a clear proximo-distal axis.     

The ultrastructure of the oenocytes in the molt/intermolt cycle of an insect

The structure and development of the permanent oenocytes of Calpodes ethlius (Lepidoptera, Hesperiidae) are described. There are three sorts of oenocyte. The permanent oenocytes are arranged ventral to the last two pairs of spiracles on abdominal segments 7 and 8 in four clusters of about 45 cells each. The molt cycle oenocytes are ventral to the other spiracles and only enlarge at molting. The subdermal oenocytes differentiate from the epidermis in large numbers shortly before pupation. The permanent oenocytes are large polyploid cells characterized by a cytoplasm of densely packed smooth tubular endoplasmic reticulum, and a plasma membrane invaginated in a meshwork of tubes ending in a reticular layer about 12 micro below the surface. There are two sorts of Golgi complex, one small and of conventional form, the other composed of clouds of microvesicles. 'Dense bodies', believed to belong to the microbody class of organelles, arise directly from the STER. There is a variety of membranous and 'crystalline' inclusions. The formation of isolation membranes from the tubular endoplasmic reticulum, and the origin of isolation bodies and autophagic vacuoles are described. Some autophagy takes place at all times in the molt/intermolt cycle, but there are phases of massive autophagy before the 4th-5th molt and the 5th-pupal molt. These phases coincide with pinocytosis of blood proteins and overlap with or are followed by phases of nuclear replication, RNA synthesis (ribosomes) and ER regeneration. Nuclear blebbing occurs before pupation. The morphology of the oenocytes is most like that of vertebrate cells engaged in steroid hormone synthesis. It is pointed out that the oenocytes rather than the prothoracic glands could be the source of ecdysone and the stimulus for molting.     

ELECTRON MICROSCOPIC OBSERVATIONS ON TUBULAR STRUCTURES INVOLVED IN CRYSTAL FORMATION IN THE RED ALGA PLEONOSPORIUM SQUARRULOSUM (HARV.) ABBOTT1

Hexagonal or angular crystalline inclusions in Pleonosporium (Naeg.) Hauck vegetative cells were examined using electron microscopy. Ultrastructural analysis reveals that the inclusions initially contain tubular elements resembling microtubules but, with continued differentiation, are transformed into rod containing crystals. The tubular structures initially measure 25 nm in diameter. Scattered tubules become arranged in a parallel and alternate pattern and undergo subsequent enlargement to approximately 29 nm. Following enlargement, each tubule apparently disaggregates into rods that form a crystal having hexagonally arranged rod-like subunits. It is suggested that these tubules may represent microtubules and the resultant crystals are composed of tubulin.     

Phylogenetic significance of the structure of adult ovary and oogenesis in a primitive chilognathan diplopod,Hyleoglomeris japonica Verhoeff (Glomerida,Diplopoda)

Some histological details of the adult ovary of Hyleoglomeris japonica are described for the first time in the glomerid diplopods. The ovary is a single, long sac-like organ extending from the 4th to the 12th body segment along the median body axis, lying between the alimentary canal and the ventral nerve cord. The ovarian wall consists of a layer of thin ovarian epithelium which surrounds a wide ovarian lumen. A pair of longitudinal “germ zones,” including female germ cells, runs in the lateral ovarian wall. Each germ zone consists of two types of oogenetic areas: 1) 8–12 narrow patch-shaped areas for oogonial proliferation, arranged metamerically in a row along each of the dorsal and ventral peripheries, and 2) the remaining wide area for oocyte growth. Oogonial proliferation areas include oogonia, very early previtellogenic oocytes, and young somatic interstitial cells, among the ovarian epithelial cells. The larger early previtellogenic oocytes in the oogonial proliferation areas are located nearer to the oocyte growth area, and migrate to the oocyte growth area. They are surrounded by a layer of follicle cells and are connected with the ovarian epithelium of the oocyte growth area by a portion of their follicles. They grow into the ovarian lumen, but their follicles are still connected with the oocyte growth area. Various sizes of the previtellogenic and vitellogenic oocytes in the ovarian lumen are connected with the oocyte growth area; the smaller oocytes are connected nearer to the dorsal and ventral oogonial proliferation areas, while the larger ones are connected nearer to the longitudinal middle line of the oocyte growth area. Following the completion of vitellogenesis and egg membrane formation in the largest primary oocytes, the germinal vesicles break down. Ripe oocytes are released from their follicles directly into the ovarian lumen to be transported into the oviducts. Ovarian structure and oogenesis of H. japonica are very similar to those of other chilognathan diplopods. At the same time, however, some characteristic features of the ovary of H. japonica are helpful for understanding the structure and evolution of the diplopod ovaries. Some aspects of the phylogenetic significance in the paired germ zones of H. japonica are discussed. J. Morphol 231:277–285, 1997. © 1997 Wiley-Liss, Inc.     

Program of F-actin in the follicular epithelium during oogenesis of the german cockroach, Blattella germanica

Extensive programmed structural and functional changes of insect follicular epithelium during oogenesis provide a model to study modulation of cytoskeletal organization during morphogenesis in a non-dividing cell population. Rhodamine-phalloidin staining of whole mounted and cryosectioned oogenic follicles reveal changing F-actin filament organization from pre- to post-vitellogenic stages consistent with the presumptive dorsal-ventral orientation of the future embryo. Filaments are not abundant in pre-vitellogenic follicle cells up to day 2. Differences between dorsal and ventral follicle cells appear first on day 3. Obviously patent follicle cells are seen only on the ventral follicle surface which exhibits stronger F-actin fluorescence than the dorsal non-patent epithelium. On the presumptive ventral side of midvitellogenic follicles morphologically distinct bundles of actin filaments orient peripherally into projections connecting adjacent follicle cells and from the center of follicle cells apically into macrovillar projections extending toward the oocyte surface. The mid-vitellogenic dorsal follicle cell layer also possesses macrovillar extensions containing F-actin which reach and appear to penetrate the oolema. During chorion deposition major reorganization of actin of follicle cells takes place. After chorion deposition all F-actin filaments within a given follicle cell are arranged into large parallel bundles with semi-regular cross-striations which exclude fluorescent label. The parallel orientation of actin striated filament bundles within each follicle cell appears to be random with respect to the orientation of bundles in neighboring follicle cells over much of the mid-latitude of the follicle epithelium. At anterior and posterior follicle poles a more axial orientation of striated bundles is evident. This muscle-like tissue arrangement is appropriate for cooperation in ovulating the chorionated oocyte from the follicle into the oviduct.     

Respiratory significance of the thoracic and abdominal morphology of Belostoma and Ranatra (insecta,heteroptera)

Summary Both Belostoma and Ranatra possess I–II, subepimeral, thoracic subalar, and abdominal subalar air stores. In Belostoma, unlike Ranatra, the subepimeral air store is greatly enlarged, the abdominal subalar store is partially exposed to the water, and a fully exposed ventral abdominal air store is also present. All the air stores of Ranatra are normally concealed.The mesothoracic and metathoracic spiracles, which open onto the I–II and subepimeral air stores respectively, are of limited permeability. They appear to have less respiratory importance than the large and highly permeable first abdominal spiracles, which lie in the subalar air space and can probably exhale and inhale large amounts of air. The large eighth abdominal spiracles, which lie at the base of the siphon or retractile organ, can also inhale or exhale much air in Ranatra but appear to be mainly exhalant in Belostoma. The smaller second through seventh abdominal spiracles structurally resemble the eighth ones in Belostoma and open onto the ventral abdominal air store. In Ranatra they appear to have no significant respiratory function.Both genera obtain atmospheric air and give off exhaled air by means of the posterior retractile organ or siphon. The two types of air appear to follow different pathways in the two genera. In Ranatra atmospheric air appears to enter the tracheal system mainly or entirely through the eighth abdominal spiracles and then passes through the first abdominal spiracles into the subalar space. Exhaled air follows the reverse pathway. In Belostoma, however, atmospheric air probably enters the tracheae mainly through the first abdominal spiracles; it is conveyed to these spiracles from the retractile organ through the subalar space or, more indirectly, through the ventral abdominal air store. Air exhaled through the first abdominal spiracles follows the reverse route; the eighth abdominal spiracles can also exhale directly into the base of the retractile organ.During underwater respiration the abdominal portion of the subalar air store appears to be the main reservoir for oxygen. The subalar oxygen is initially atmospheric, and is supplemented, during submersion, by other sources of oxygen. Belostoma may use its exposed ventral abdominal air store, and its partially exposed abdominal subalar one, as physical gills; both these stores communicate with the inhalant first abdominal spiracles. Ranatra, none of whose air stores are normally exposed, appears, to be less capable of utilizing dissolved oxygen, but the considerable amount of atmospheric oxygen in the elongated siphon may be inhaled, during submersion, through the eighth abdominal spiracles.In both genera the thoracic air stores appear to be of less respiratory importance than the abdominal ones. They do not appear capable of obtaining large amounts of oxygen, and the thoracic spiracles are relatively impermeable. All the air stores, however, serve to protect the spiracles against the entry of water, and also contribute to the body's hydrostatic balance. It is also possible that some of the air stores play a role in pressure reception.The literature indicates much intergeneric variation in the respiration of Belostomatidae and Nepidae. In the Belostomatidae there is considerable variation in the extent of the ventral abdominal air store and in the roles of the subalar air store and the spiracles. The Nepidae show differences in their ability to utilize dissolved oxygen and in the extent of the subepimeral air store.     

Involution of seminiferous tubules in aged hamsters: an ultrastructural, immunohistochemical and quantitative morphological study

In this study, we examined the age-related changes on morphometric parameters and ultrastructure of seminiferous tubules, and on the expression of extracellular matrix proteins in lamina propria of Syrian hamsters. A significant decrease in the percentage of normal tubules and an increase in the percentage of hypospermatogenic and arrested maturation tubules was observed with aging. Aged animals showed a decrease in tubular diameter, tubular lumen, seminiferous epithelium volume and total tubular volume. However, the total length of seminiferous tubules was significantly increased with aging. The most important ultrastructural changes with aging were the thickening of the lamina propria, the presence of diverse abnormalities in the spermiogenesis process, degeneration of germ cells, and vacuolization and flattening of Sertoli cells showing abundant lipofucsin droplets and residual bodies. Laminin immunoreactivity was found along the lamina propria of seminiferous tubules both in young and aged animals. Fibronectin immunoreactivity was found along the lamina propria and blood vessels. Both laminin and fibronectin total volume of immunostaining per testis was increased in aged hamsters. In conclusion, the age-related changes in seminiferous tubules of hamster include: a decrease in tubular width and an increase in tubular length; widening of the lamina propria caused by a more extensive connective matrix between the peritubular cells and the basal membrane; and a strong disarrangement of the seminiferous epithelium, including germ cell degeneration and important alterations in both spermiogenesis and Sertoli cell structure.