Acrosomal Complex Research Articles

Ultrastructure of the spermatozoon of the tuatara ( Sphenodon punctatus ) and its relevance to the relationships of the Sphenodontida

Spermatozoa of the New Zealand tuatara , Sphenodon punctatus punctatus (Gray), are described from light and electron microscopic observations and compared with spermatozoa of other living ‘reptiles’ (Chelonia, Crocodilia, Squamata), birds and mammals. Mature Sphenodon spermatozoa consist of an acrosomal complex (length 4 µm), elongate, helical nucleus (54-56 µm), a relatively short midpiece (7-8 µm), elongate principal piece (74-78 µm) and short end piece (2-4 µm). The acrosomal vesicle and underlying subacrosomal material form a double, curved, conical sheath around the nucleus anteriorly. Two parallel, loosely helical, endonuclear canals each containing perforatorial material, extend posteriorly from the apex of the nucleus to at least 2.5 µm below the base of the acrosomal complex. Rings of several spherical mitochondria are stacked around the elongate distal centriole to form the midpiece. Each mitochondrion has concentric cristae surrounding a dense central body. Proximal and distal centrioles, although differing markedly in length, are similar in having triplets with an open C tubule. Nine peripheral fibres are intimately associated with the triplets of the distal centriole. A well developed annulus defines the posterior extremity of the midpiece. The principal piece consists of a 9 + 2 axoneme (accompanied anteriorly by nine peripheral fibres) surrounded by a highly electron-dense fibrous sheath and the plasma membrane. Absence of a penis in Sphenodon has not resulted in recognizable modifications of the spermatozoon. Sphenodon shares many spermatozoal features here interpreted as plesiomorphies with crocodiles and turtles, particularly the latter group, but exhibits none of the advanced character states (apomorphies) diagnostic of the Squamata. These data not only underscore the primitive status of living tuatara (recently questioned in the literature) but also militate against a close, sister-group relationship between the Sphenodontida and Squamata.

Distribution of sugar residues in the bovine testis during postnatal ontogenesis demonstrated with lectin-horseradish peroxidase conjugates.

In the present study the distribution of various sugar residues in the cells of the male gonad during postnatal organogenesis was examined employing eight lectin-horseradish peroxidase conjugates (BS-I, ConA, DBA, PNA, RCA-I, SBA, UEA-I, WGA) on paraffin-embedded testicular tissue. The tissue was obtained from bull calves and young bulls of recorded age (4, 8, 16, 20, 25, 30, 40 and 52 weeks) and two adult bulls. During the whole observation period, lectin affinity in the developing testicular tubules was restricted to the germ cell line, while the Sertoli cells and their precursors remained completely unstained. DBA, a lectin with specific affinity to alpha-D-GalNAc, served as a selective marker for prespermatogonia (PSG), the only precursors of bovine spermatogonia until the onset of spermatogenesis at week 30. alpha-D-GalNAc, detected in the PSG Golgi zone and its vicinity, seems to play an important role during PSG proliferation and migration in the prepuberal testis. Concomitant with the differentiation of PSG into spermatogonia, the binding intensity of DBA to the Golgi zone of these cells decreased. After the gradual onset of spermatogenesis, the lectins revealed staining of Golgi complexes of most germ cell stages. Glycosylation of the cell components takes place in the Golgi complex, which explains the strong affinity of the lectins to this cell compartment. Inner and outer membrane of the acrosomal complex of spermatids, especially during Golgi and cap phase of spermiogenesis, were intensely stained with PNA, RCA-I and SBA. This staining disappeared in the maturation phase at the latest and indicates a role of terminal D-Gal-(beta 1----3)-D-GalNAc, D-Gal and D-GalNAc during the formation of the sperm head and intraepithelial orientation of the spermatid. Other parts of the spermatid, such as the anulus and the cytoplasmic droplet, exhibited D-Gal, D-GlcNAc or sialic acid and D-GalNAc. In the intertubular tissue BS-I, RCA-I and UEA-I bound to vascular endothelia. Components of the intertubular extracellular matrix were stained with ConA (alpha-D-Man), RCA-I (D-Gal), UEA-I (alpha-L-Fuc) and WGA (D-GlcNAc or sialic acid).

Fine structure of the spermatozoon of the sandflySergentomyia minuta(Diptera, Psychodidae)

Abstract Spermatozoa of Sergentomyia minuta were examined by light, scanning, and transmission electron microscopy. They were seen to be formed by a head and a tail. The head was characterized by an acrosomal complex with a thin space containing granular material organized as in a perforatorium. The tail contained a “9 + 9 + 0”; axoneme and one mitochondrial derivative. A comparison with the spermatozoon ultrastructure of other Diptera, particularly Psychodidae, is discussed.

Linkage of manchette microtubules to the nuclear envelope and observations of the role of the manchette in nuclear shaping during spermiogenesis in rodents

Structural features of the mouse and rat manchette and the role of the manchette in shaping the spermatid nucleus were investigated. Rod-like elements about 10 nm in diameter and 40-70 nm in length were seen linking the innermost microtubules of the manchette and the outer leaflet of the nuclear envelope in step 8 through step 11 rat and mouse spermatids that either had been routinely fixed for electron microscopy or had been isolated and detergent extracted. Rod-like linkers were also seen joining the nuclear ring to the plasma membrane and nuclear envelope. These linkers may ensure that under normal conditions the manchette remains in a defined position relative to these membranous components. A variety of compounds (taxol, cytoxan, and 5-fluorouracil) were found to perturb the manchette and to affect nuclear shaping. In addition, sys and azh mutant mice were used to determine the consequences of defective manchette formation. These genetic conditions and chemical treatments either produced manchettes that were not in their normal position (azh, sys, and taxol) and/or caused the manchette to appear abnormal (azh, sys, cytoxan, 5-fluorouracil, and taxol), and all resulted in a deformation of the step 9-11 spermatid nucleus. In all instances where the manchette was present, either in normal or ectopic locations, the sectioned nuclear envelope was parallel to the long axis of the microtubules of the manchette. In general, areas of the nuclear envelope where the manchette was not present, or where it was expected to be present but was not, were rounded (normal animals, sys, cytoxan). In addition, there are indications using certain compounds (cytoxan and 5-fluorouracil) as well as in the azh and sys mouse that the manchette may exert pressure to deform the nucleus. It is suggested that the rod-like linkages of the manchette ensure that the nuclear envelope remains at a constant distance from the manchette microtubules and that this is a major factor acting to impart nuclear shape changes on a region of the head caudal to the acrosome during the early elongation phase of spermiogenesis. The manchette microtubules, which are also known to be linked together, may act as a scaffold to deform this part of the nucleus from its spherical shape, perhaps in concert with forces initiated by other structural elements. Evidence from sys animals indicates that structural elements, such as the acrosomal complex over the anterior head (acrosome-actin-nuclear envelope), may affect nuclear shaping over the acrosome-covered portion of the spermatid head.(ABSTRACT TRUNCATED AT 400 WORDS)

Euspermatozoa and paraspermatozoa in the trochoid gastropodZalipais laseroni (Trochoidea: Skeneidae)

Pronounced sperm dimorphism is reported for the first time in the prosobranch order Vetigastropoda. Using transmission electron microscopy, it is demonstrated thatZalipais laseroni Kershaw (Trochoidea: Skeneidae) produces uniflagellate euspermatozoa (eupyrene, fertile sperm) and multiflagellate paraspermatozoa (oligopyrene, infertile sperm). Euspermatozoa show the following features: (1) a conical acrosomal vesicle; (2) a long tubular, helically coiled nucleus; (3) a short midpiece (mitochondrial sleeve surrounding a 3µm-long electron-dense rod); (4) a chambered body (? fused centrioles) continuous with the dense rod of the midpiece; (5) a flagellum (characterized by an electron-dense sheath surrounding and partly obscuring the central pair of tubules). Paraspermatozoa are composed of an elongate head (lacking an acrosomal complex), a short midpiece (centriolar rods interspersed with mitochondria), and a posterior tuft of flagella. The head consists of a rodshaped anterior body and a condensed nuclear remnant — the latter lodged in a shallow invagination of the anterior body. Multiple flagella are attached via centriolar rods to a layer of dense material lining the nuclear remnant membrane. During paraspermatozoan development, the nucleus partially degenerates, then condenses, while the endoplasmic reticulum (ER), apparently assisted by the Golgi complex, is responsible for production of numerous, electron-dense secretory vesicles. These vesicles subsequently fuse to form the elongate, anterior body of the head region. The ability of at least one line of trochoid gastropods to produce an oligopyrene, multiaxonemal paraspermatozoon, suggests that the Caenogastropoda (with this feature) might have been derived from the Vetigastropoda rather than from any other archaeogastropod source.

Actin filaments in two spermatozoa of crustacea decapoda

Sperm of decapod crustaceans are formed by a round or cup-shaped body, a complex acrosome and one a few appendages emerging from the main body. Although this sperm does not have motility, it has some components of the cytoskeleton like microtubules, which are found inside the appendages. Actin filaments have been found in the spike of penaeidae sperms. The actual participation of the crustacean decapod sperm cytoskeleton during fertilization is not well understood. Actin is supposed to play an active role in drawing the penaeidae shrimp sperm closer to the egg after bending of the spike. The present study was aimed at the localization of actin filaments in sperm of the Robinson Crusoe island lobster, Jasus frontalis and in the crayfish Orconectes propincus, by fluorescent probes and low voltage scanning electron microscopy.

Spermiogenesis and sperm ultrastructure in the freshwater musselDiplodon chilensis chilensis(Mollusca: Bivalvia)

Summary Spermiogenesis and sperm ultrastructure of Diplodon chilensis chilensis have been studied. Early spermatids show some peculiar characteristics which include scanty cytoplasm mitochondria restricted to a juxtanuclear region and a poorly developed Golgi complex, a feature present throughout spermiogenesis. Mid and late spermatids show an elongated nucleus and a granular pattern of chromatin condensation. The Golgi complex does not show changes associated to the formation of structures of the acrosomal complex. The mature spermatozoon agrees in all main features with those of bivalves with external fertilization. It is thus of the primitive type with bullet-shaped nucleus and five mitochondrial spheres in the middle piece. The head of the mature sperm lacks acrosomal structures. Previously reported modifications in the reproductive biology of D. ch. chilensis with respect to aspects considered representative of bivalves, have not brought about major modifications in sperm morphology.

Ultrastructure of the Geogarypus nigrimanus Spermatozoon (Arachnida, Pseudoscorpionida)

AbstractThe ultrastructure of the spermatozoon of Geogarypus nigrimanus (Arachnida, Pseudoscorpionida) is described. The spermatozoon is composed of a small elliptic nucleus, a short flagellum and a very long and complex acrosome. In the male genital ducts, as in other studied species of pseudoscorpions, the sperm components are rolled up to form a globular structure enclosed in a cyst wall. The Geogarypus spermatozoon with a reduced flagellum and a giant acrosome seems to be evolutionary more advanced than spermatozoa from other pseudoscorpions.

Spermiogenesis and spermatozoa in the relict bivalve genus Neotrigonia: relevance to trigonioid relationships, particularly Unionoidea

Spermiogenesis and spermatozoa in the relict trigonioid genus Neotrigonia are examined ultrastructurally. Mature Neotrigonia spp. spermatozoa exhibit the following features: (1) a blunt-conical nucleus; (2) an acrosomal complex composed of discoidal vesicles (9 to 15) arranged as a thin layer over the nuclear apex; (3) five (rarely four) spherical mitochondria positioned in depressions at the base of the nucleus; (4) proximal and distal centrioles (surrounded by the mitochondria); (5) a satellite complex anchoring the distal centriole and flagellum to the plasma membrane; and (6) a single flagellum. Spermatozoa of unionoids examined to date (Unionidae and Hyriidae only) exhibit similar features, including a nucleus with a blunt apex capped by a thin acrosomal complex (showing up to three vesicles). Among the Bivalvia, only Neotrigonia spp. and unionoid sperm possess an acrosomal complex composed of multiple vesicles. These data suggest that the Trigonioidea and Unionoidea are phylogenetically linked, but further work particularly on primitive unionoids is required to determine if this relationship is one of common ancestry or whether the Unionoidea have in fact been derived from the Trigonioidea.

Ultrastructure of spermiogenesis in the gastropod Calliotropis glyptus Watson (Prosobranchia: Trochidae) with special reference to the embedded acrosome.

Testicular spermatozoa and sperm development in the archaeogastropod Calliotropis glyptus Watson (Trochoidea: Trochidae) are examined using transmission electron microscopy and formalin-fixed tissues. During spermiogenesis, the acrosome, formed evidently through fusion of Golgi-derived proacrosomal vesicles, becomes deeply embedded in the condensing spermatid nucleus. Two centrioles (proximal and distal), both showing triplet microtubular substructure, are present in spermatids--the distal centriole giving rise to the sperm tail and its associated rootlet. During formation of the basal invagination in the spermatid nucleus, centrioles, and rootlet move towards the nucleus and come to lie totally within the basal invagination. Mitochondria are initially positioned near the base of the nucleus but subsequently become laterally displaced. Morphology of the mature spermatozoon is modified from that of the classic primitive or ect-aquasperm type by having 1) the acrosome embedded in the nucleus (the only known example within the Mollusca), 2) a deep basal invagination in the nucleus containing proximal and distal centrioles and an enveloping matrix (derived from the rootlet), 3) laterally displaced periaxonemal mitochondria, and 4) a tail extending from the basal invagination of the nucleus. Implantation of the acrosomal complex and centrioles within invaginations of the nucleus and lateral displacement of mitochondria effectively minimize the length of the sperm head and midpiece. Such modifications may be associated with motility demands, but this remains to be established. The unusual features of C. glyptus spermatozoa, though easily derivable from "typical" trochoid sperm architecture, may prove useful in delineating the genus Calliotropis or tracing its relationship to other genera within the trochid subfamily Margaritinae.

Membrane specializations associated with the acrosomal complex of sea urchin sperm as revealed by immunocytochemistry and freeze fracture replication.

Observations, employing freeze fracture replication and electron microscopic immunochemistry, have been carried out to determine structural correlations of the plasma membrane domain occupied by a 210 kDa protein involved in the acrosomal reaction of sea urchin sperm and recognized by the monoclonal antibody, J10/14 (Trimmer et al.: Cell 40:697-703, 1985; Proceedings of the National Academy of Sciences of the United States of America 83: 9055-9059, 1986). Immunogold-J10/14 staining of acrosome-intact sperm was intense along the flagellum and a narrow collar just posterior to the sperm apex that surrounded the acrosomal complex (acrosomal vesicle and subjacent anterior nuclear fossa containing g-actin). Counts of gold particles revealed a density (average number of particles/micron2 of surface area) eightfold greater along the plasma membrane associated with the acrosomal complex than membrane delimiting the remainder of the sperm head. The collar of J10/14 staining was isomorphic with a dense aggregation of intramembranous particles in the P-face of the plasma membrane and a thin cytoplasmic region that surrounded the acrosomal complex. In acrosome-reacted sperm, intense J10/14 staining was distributed along the flagellum and sperm head; prominent anterior staining was not apparent in all specimens. The density of gold particles associated with plasma membrane delimiting components of the former acrosomal complex, nucleus and mitochondrion, as well as the total average number of particles along the entire sperm surface, were increased in sperm acrosome-reacted with A-23187. Concomitant with this change in staining was the disappearance/reduction of the collars of intramembranous particles and cytoplasm. These observations indicate that plasma membrane components (210 kDa protein and intramembranous particles) and the collar of cytoplasm which are associated with the acrosomal complex are functionally, as well as structurally related. Analyses of particle density distributions along acrosome- and non-acrosome-reacted sperm suggest that the different staining patterns observed may be brought about by the recognition of cryptic sites at the time of the acrosomal reaction.

Immotile, aflagellate spermatozoa in Ptiliidae coleopterans

The first aflagellate and immotile Coleopteran spermatozoon is described in a group of species belonging to the family Ptiliidae. The mature spermatozoon is devoid of flagellum, centrioles and mitochondria, includes a three‐layered acrosomal complex (extraacrosomal layer, acrosome and perforatorium) and a long nucleus made up of two regions of different densities. A compact submembranary capsule and a thick glycocalyx are also present. Motility organelles are absent during the whole spermiogenesis, which is not regressive. The new structures peculiar for this type of sperma are designed for protection. No other sperm models with these characteristics have been described so far.

Immotile, aflagellate spermatozoa in Ptiliidae coleopterans

The first aflagellate and immotile Coleopteran spermatozoon is described in a group of species belonging to the family Ptiliidae. The mature spermatozoon is devoid of flagellum, centrioles and mitochondria, includes a three-layered acrosomal complex (extraacrosomal layer, acrosome and perforatorium) and a long nucleus made up of two regions of different densities. A compact submembranary capsule and a thick glycocalyx are also present. Motility organelles are absent during the whole spermiogenesis, which is not regressive. The new structures peculiar for this type of sperma are designed for protection. No other sperm models with these characteristics have been described so far.

REPRODUCTIVE SYSTEM OF THE PARASITIC COPEPOD PACHYPYGUS GIBBER: SPERMATOGENESIS AND SPERMATOPHORE FORMATION IN DIMORPHIC MALES, AND DISCHARGE IN FEMALE TRACTS

ABSTRACT An ultrastructural comparison of the spermatogenesis of dimorphic males of Pachypygus gibber has been made. After maturation, the spermatozoon is identical in the two males. It appears as a cell in which nucleoplasm and cytoplasm are mixed, with an important densification zone composed of a homogeneous zone and a zone with a paracrystalline organization. The nature of this structure recalls an acrosomal complex. An original feature is the wrapping of the spermatozoon around a vesicle which could have either a nutritive role or a role as sperm carrier involved in the transport to the female genital tracts. Data concerning the copulatory behavior of the two males and of the female genital system are given. The modifications of the sperm observed in the female tracts could be linked to capacitation mechanisms before fertilization. We conclude that the different steps in spermatogenesis are the same in the two males of Pachypygus and that they lead to only one type of spermatozoon and consequently to only one type of fertilized egg.

Spermiogenesis inChalcides ocellatus tiligugu(Gmelin) (Squamata, Scincidae): An electron microscope study

Abstract At the end of spermiogenesis in Chalcides ocellatus tiligugu the acrosomal complex is constituted by a homogeneous anterior cap derived from the acrosomal vesicle and by a paracrystalline posterior cap that arises from nuclear membrane proliferation. During the spermiogenetic process, the spherical nucleus becomes elongated and cylindrical in shape, and assumes a homogeneous appearance because its chromatine condenses. At the onset of spermatid elongation, a set of microtubules appears as a helix surrounding the nucleus. At the end of elongation, the microtubules become parallel to the main axis of the nucleus. From the early stage of spermiogenesis, the two centrioles (proximal and distal) and the flagellum are situated at the posterior pole of the nucleus. The two centrioles are encircled by the dense connecting piece, which is continuous with the nine accessory fibers surrounding the flagellum. At a later stage, the mitochondria form the mitochondrial sheath and four rings of electron‐dense ma...

The ultrastructure of spermatozoa and spermiogenesis in pyramidellid gastropods, and its systematic importance

Ultrastructural observations on spermiogenesis and spermatozoa of selected pyramidellid gastropods (species ofTurbonilla, Pyrgulina, Cingulina andHinemoa) are presented. During spermatid developement, the condensing nucleus becomes initially anterio-posteriorly compressed or sometimes cup-shaped. Concurrently, the acrosomal complex attaches to an electrondense layer at the presumptive anterior pole of the nucleus, while at the opposite (posterior) pole of the nucleus a shallow invagination is formed to accommodate the centriolar derivative. Midpiece formation begins soon after these events have taken place, and involves the following processes: (1) the wrapping of individual mitochondria around the axoneme/coarse fibre complex; (2) later internal metamorphosis resulting in replacement of cristae by paracrystalline layers which envelope the matrix material; and (3) formation of a glycogen-filled helix within the mitochondrial derivative (via a secondary wrapping of mitochondria). Advanced stages of nuclear condensation (elongation, transformation of fibres into lamellae, subsequent compaction) and midpiece formation proceed within a microtubular sheath (‘manchette’). Pyramidellid spermatozoa consist of an acrosomal complex (round to ovoid apical vesicle; column-shaped acrosomal pedestal), helically-keeled nucleus (short, 7–10 μm long, shallow basal invagination for axoneme/coarse fibre attachment), elongate helical midpiece (composed of axoneme, coarse fibres, paracrystalline and matrix materials, glycogen-filled helix), glycogen piece (length variable, preceeded by a dense ring structure at junction with midpiece). The features of developing and mature spermatozoa observed in the Pyramidellidae are as observed in opisthobranch and pulmonate gastropods indicating that the Pyramidelloidea should be placed within the Euthyneura/Heterobranchia, most appropriately as a member group of the Opisthobranchia.

ULTRASTRUCTURE OF THE SPERM AND SPERMATOPHORES OF THE GOLDEN CRAB GERYON FENNERI AND A CLOSELY RELATED SPECIES, THE RED CRAB G. QUINQUEDENS, FROM THE EASTERN GULF OF MEXICO

The sperm of species of Geryon are typical of brachyurans in having a complex acrosome, a membranous lamellar complex, uncondensed chromatin in the nucleus, and nuclear arms or spikes of varying lengths. There are no microtubular elements in the arms. The spermatophores are ellipsoidal or round and contain varying numbers of sperm. The wall of each spermatophore is two-layered and fairly impermeable to fixatives. Globules of seminal fluid surround the spermatophores in the vasa deferentia. The golden crab Geryonfenneri Manning and Holthuis, 1984, is a nonswimming brachyuran from deep water in the eastern Gulf of Mexico. Relatively little is known about the reproductive biology of the golden crab or a related species, the red crab G. quinquedens Smith, 1879. The golden crab is a recently described species (Manning and Holthuis, 1984) and supports a newly established commercial fishery. Though many studies have been made of the sperm of other brachyurans, no ultrastructural studies have been made of the sperm of the genus Geryon. In this study, the morphological structure of the sperm of G. fenneri and G. quinquedens is examined and compared with that of other crustaceans.

Ultrastructure des spermatozoides des males haploides et diploides de Diadromus pulchellus wesmeal (Hymenoptera : Ichneumonidae)

The mature spermatozoa were described in the haploïd and diploïd males of Diadromus pulchellus Wesmeal (Hymenoptera : Ichneumonidae). Diploïd males produce spermatozoa, which do not seem to be different from those produced by haploïd males. The spermatozoon is about 100 μm long, and consists of a head, 0.8 μm in diameter, and a tail 0.3 μm in diameter. Its anterior part shows an acrosomal complex, including a perforatorium and a compact and electron-dense fusiform nucleus. The postnuclear region includes a longitudinal axoneme with 2 mitochondrial derivatives. The axoneme shows 2 typical central units, 9 peripheral doublet microtubules, 9 accessory internal tubules, and 9 external microtubules with dense contents. In the testes of diploïd males, a great number of abnormal spermatozoa were observed. These spermatozoa with degenerative structures are probably not implicated in egg fertilization.

Spermatozoa and phylogeny of Curculionoidea (Coleoptera)

In the examined families of Curculionoidea (Coleoptera), the sperm, although characteristic of typical pterygote insects, shows a few peculiarities that suggest Curculionoidea to be a homogeneous group. The curculionid sperm, in fact, always follows a similar structural design, without any variation. For example, it has 2 mitochondrial derivatives of different sizes, the larger of which is almost completely filled with a crystalline protein, the other being more moderately crystallized and almost completely occupied by cristae, and 2 accessory bodies of different sizes that are made up of a crystalline portion, crescent-shaped in section, and a “puff”-like expansion that is of different consistency, shape, and symmetry in various cases. The different extensions of the accessory bodies seem, therefore, to compensate for the high degree of asymmetry due to the largely different sizes of the 2 mitochondrial derivatives. The examined families and subfamilies can be arranged in 2 groups: Rhynchitidae appear drastically isolated, because they have a peculiar “9 + 9 + 0” axoneme, and show, moreover, a limited degree of asymmetry in the tail organelles. The remaining families and subfamilies are more closely related to one another by the presence of a “9 + 9 + 2” classical axoneme and by the same degree of asymmetry in the tail, typical of curculionid sperm. Among them, Apionidae are distinguished for the space containing the extraacrosomal layer, which may be hollow or absent, a twice-stepped nucleus-tail connection, and a thick glycocalyx at the end of the tail. The Curculionidae conserve primitive characters, such as the 3-layered acrosomal complex and “9 + 9 + 2” axoneme, but also present a high degree of differentiation in the shape of the asymmetrical tail organelles. There appear to be 3 clusters: the first cluster includes Brachyderinae, Leptopiinae, Gymnetrinae, Cryptorhynchinae, Rhynchophorinae. The second cluster includes Scolytidae, Cleoninae, Hylobiinae. The third cluster is more numerous and heterogeneous and shows 3 subgroups. The first of these includes only Otiorhynchinae. The sum of their characters shows that they have most of the common features of primitive curculionids; however the differences between a genus and another are so large that they could be assigned to different subfamilies. The second subgroup includes Hyperinae, Pissodinae, Magdalinae, Ceutorhynchinae and Cossoninae, and the third group includes Cioninae, Anthonominae, and Barimae. It is difficult to arrange these subfamilies (frequently recognizable for a different combination of the same recurrent characters) in a phylogenetic tree. However, we observed signs of primitiveness in Brachyderinae (small crescents) and their cluster; advanced ones in the third and fourth clusters all evolved with different patterns of the puff-like expansion of one of the accessory bodies, the latter being the most peculiar character of the superfamily. A tentative reconstruction is given. The functional significance of the variations seems to be that Rhynchitidae seem to be evolving towards immotility (their spermatozoon, in fact, is able to produce only a series of vibrations, not the progressive series of waves as in all other species studied), while all the other families and subfamilies show no signs of alterations in axonemal pattern and motility. The main evolutionary pathways observed in them are towards compensating for an exaggerated lengthening and a greater degree of asymmetry in the tail organelles: one of them, the major mitochondrial derivative, acts as a rigid axis, while the axoneme produces undulations in the opposite portion of the axonemal section.

Fine structure of spermatozoa and spermatogenesis ofSchizomus palaciosi, Reddell and Cokendolpher, 1986 (Arachnida: Uropygi, Schizomida)

Spermatogenesis ofSchizomus palaciosi occurs in cysts in paired tubular testes located ventrally in the opisthosoma. Only few germ cells comprise one cyst. In early spermiogenesis an acrosomal complex composed of a spherical vacuole and a short acrosomal filament is established opposite of which a 9×2+3 flagellum emerges from a flagellar tunnel. The latter, however, is only a short-lasting structure. A manchette of microtubules surrounds nucleus and part of the acrosomal vacuole. The alterations in the arrangement of the microtubules during spermiogenesis are described. The spermatid finally is an elongate cell with a slender acrosomal vacuole on top of the helical nucleus. A deep implantation fossa filled with dense material is encountered. The acrosomal vacuole is accompanied by an intricate paracrosomal lattice structure not known at present of otherArachnida. This structure disappears during final spermiogenesis. The acrosomal filament (perforatorium) reveals filamentous subunits arranged in a regular pattern. Large ovoid mitochondria do not establish a distinct middle piece. Finally the elongate spermatid is coiled to form the mature spherical spermatozoon.