FUNGAL REMAINS IN THE DEVONIAN TRIMEROPHYTE PSILOPHYTON DAWSONII

Fungal reproductive structures were found within aerial axes of the Late Devonian trimerophyte, Psilophyton dawsonii Banks, Leclercq and Hueber from Quebec, Canada. Specimens are spherical to oval, up to 175 μm in maximum diam, and exhibit two distinct wall layers. They are restricted to the inner cortical region of infected axes. The fungal bodies resemble species of Palaeomyces from the well-known Rhynie Chert flora, and are also similar to the chlamydospores commonly found in Pennsylvanian coal ball plants. Among extant organisms they are most similar to oomycetous oogonia and endogonaceous chlamydospores.     

Euspermatozoa,Paraspermatozoa and Spermatozeugmata of Littoraria (Palustorina) articulata (Prosobranchia: Caenogastropoda) with Special Reference to the Pseudotrich

Abstract Paraspermatozoa and euspermatozoa of the littorinid gastropod Littoraria (Palustorina) articulata are examined using transmission electron microscopy and light microscopy. In the seminal vesicle, both sperm types occur, either as free cells or organized into spermatozeugmata. It is shown that the elongate (120–140 μm), flagellum-like component of the paraspermatozoon is in fact a tubular extension of the plasma membrane which encloses granular material but no axonemes or microtubules. This structure, here termed the pseudotrich, shows no evidence of motility and its function remains obscure. The main body region of the paraspermatozoon (length 32–36 μm) contains numerous spherical vesicles, scattered mitochondria, one or two large, rod-shaped bodies (length 20–24 μm) and a fusiform, granular body (containing DNA; probably a modified nucleus). The rod-shaped bodies, granular body and surrounding matrix are contained by a common membrane, and are therefore separated from other contents of the paraspermatozoon. In each spermatozeugma, euspermatozoa are attached via the tips of their acrosomes to the paraspermatozoan body at the opposite end to the pseudotrich. Euspermatozoa exhibit a conical acrosomal complex (with axial rod and basal plate), a tubular nucleus sheathing the axoneme, a midpiece (5–6 helical mitochondrial elements sheathing the axoneme), an annulus (with two rings), a glycogen piece and an end piece (total sperm length 268–272 μm). The euspermatozoa of L. articulata are similar to those of most littorinids and many other caenogastropods. The presence of a pseudotrich in the paraspermatozoon appears to be restricted to the subgenus Palustorina.     

COMPARATIVE ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE METZGERIALES (HEPATICAE). I. THE BLEPHAROPLAST OF PALLAVICINIA LYELLII

The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in that it comprises a four-layered multilayered structure (MLS) and two staggered, dimorphic basal bodies. The spline, approximately 40 μm in length and extending through nearly two full gyres, comprises 20 parallel microtubules at its anterior end and narrows to 17 at the posterior limit of the subjacent lamellar strip (LS). Behind this, the spline shank, approximately 32 μm in length, is reduced to six tubules. The LS curves around the spermatid, following the anterior one-third of the first gyre of the spine, and is approximately 7.5 μm in length, the longest yet recorded for the bryophytes. It is spatulate in outline, equaling the width of the spline anteriorly but tapering steeply from the right-hand side behind the anterior basal body (ABB). It then extends posteriorly as a narrow strip beneath the left-hand margin of the spline. The basal bodies of the greatly staggered flagella are nonoverlapping and separated by a distance of about 4.4 μm. The subapical ABB and PBB measure (including the ventral triplet extensions and transition zones) 1.2 μm and 2.4 μm in length, respectively. A short, narrow aperture equaling one tubule-diameter in width is located in the spline directly beneath the ABB. The anterior mitochondrion is about 7 μm long and follows the outline of the overlying LS, while a cupshaped posterior mitochondrion is appressed to the plastid. Comparisons with other taxa indicate that major distinguishing features of metzgerialian blepharoplasts are highly staggered, nonoverlapping basal bodies, greatly elongate anterior mitochondria, and six-tubule shanks. Great differences between the spermatids suggest wide phylogenetic discontinuities between the genera of the Metzgeriales.     

Three New Species of Eimeria (Apicomplexa: Eimeriidae) from Nerodia rhombifem (Serpentes: Colubridae) from Texas1

Three new species of Eimeria (Apicomplexa: Eimeriidae) are described from the intestinal contents of Nerodia rhombifera (Serpentes: Colubridae) from Texas. Oocysts of Eimeria infirmus are irregular in shape, 11.6 (8.8–14.4) μm in diameter, with a smooth, thin wall that ruptures easily, releasing free sporocysts. A small polar granule is usually present, but a micropyle and oocyst residuum are absent. Sporocysts are bean-shaped with one side flattened slightly, 9.1 times 5.0 (7.2–10.4 times 4.4–5.8) μm, with what may be a Stieda body consisting of a slight thickening of one end of the sporocyst. Each sporocyst contains a spherical or ellipsoid residuum and sporozoites, each with a single, posterior refractile body. Oocysts of Eimeria rhombifera are spherical or subspherical, 13.1 times 12.6 (12.0–14.4 times 11.2–14.4) μm, with a smooth, frail wall. A polar granule is present, but a micropyle and oocyst residuum are absent. Sporocysts are ovoid, 8.8 times 5.5 (8.0–9.6 times 5.0–6.0) μm, each with a Stieda body. Each sporocyst contains a spherical or subspherical residuum and sporozoites, each with a single posterior refractile body. Oocysts of Eimeria tenuis are ellipsoidal in shape, 17.2 times 10.8 (15.2–20.8 times 9.6–12.0) μm, with a smooth, thin wall. A polar granule and oocyst residuum are present, but a micropyle is absent. Sporocysts are elongate, 13.2 times 4.9(11.2–15.2 times 4.4–5.6) μm, each with a Stieda body consisting of a thickening of the sporocyst wall. Each sporocyst contains a spherical or subspherical residuum and sporozoites with anterior and posterior refractile bodies.     

Scanning electron microscopic investigation of the spermatophore and spermatozoa of the shrimp Farfantepenaeus subtilis (Decapoda: Penaeidae)

Scanning electron microscopy was used to describe the structure of the spermatozoon and spermatophore of Farfantepenaeus subtilis. The spermatophore showed characteristics similar to those of members of the subgenus Farfantepenaeus. This included an extensive glandular epithelium and a lack of a wing. The sperm mass, which was distributed at the periphery of the spermatophore, was surrounded by a large amount of acellular material. The spermatozoon has a spherical main body and a well-defined acrosomal region with a single spike, which was bent in some cells. The immotile sperm cells have an average length of 7.1?±?0.6?μm. Information on sperm location within the spermatophore will assist in the efficient extraction of the sperm mass during dissection.     

Breakdown of the cortical alveoli of medaka eggs at the time of fertilization,with a particular reference to the possible role of spherical bodies in the alveoli

Summary The process of cortical change upon fertilization of eggs of the teleostean fish,Oryzias latipes was investigated. A cortical alveolus (CA) contains colloidal material, a spherical body, and often a membranous structure. Upon insemination, breakdown of the cortical alveoli and elevation of the chorion began around the animal pole and ended at the vegetal pole. It was found that the spherical body was extruded with the colloidal material from the CA: the spherical body swelled after the opening of an aperture and was extruded into the perivitelline space through a large aperture. The empty CA shrank and disappeared completely as a result of the transformation of its envelope to numerous microvilli. The spherical body isolated or in the perivitelline space could be digested quickly by proteolytic enzymes. When spherical bodies in the perivitelline space of a fertilized egg were digested enzymatically, the vitellus came into direct contact with the chorion. The present study seems to show that swollen spherical bodies derived from CA play a role in maintaining a certain distance between the chorion and the vitellus after fertilization.     

An electron microscope study of gametangia in the green seaweed Halimeda tuna

Abstract

The gametangia of the green seaweed Halimeda tuna are spherical bodies of diameter up to 250–300 μm. They are clustered in groups of 8–10 on hundreds of threads sprouting from all pale white segments of the fertile individuals. In addition to gametes, starch-containing chloroplasts, naked starch grains and two types of spherical bodies different in size and ultrastructure are the main corpuscular components. A layer of amorphous material of irregular thickness underlies the walls which are finely and evenly rough, structureless, electron translucent and 1–1.5 μm thick. Gametangia with superficial wall warts were found also.     

Three new species of <Emphasis Type="Italic">Isospora</Emphasis> Schneider, 1881 (Apicomplexa: Eimeriidae) from the buffy-fronted seedeater <Emphasis Type="Italic">Sporophila frontalis</Emphasis> Verreaux (Passeriformes: Emberizidae) in South America

Three new coccidian (Apicomplexa: Eimeriidae) species from the buffy-fronted seedeater Sporophila frontalis Verraux in Brazil are reported in the current study. Isospora frontalis n. sp. oöcysts are spherical to sub-spherical, 27.9 × 26.9 μm, with a smooth, bi-layered wall c.1.4 μm thick. A micropyle and an oöcyst residuum are absent, but polar granules are present. Sporocysts are elongate ellipsoidal, 19.6 × 11.1 μm. The Stieda body is knob-like and the substieda body is slight. The sporocyst residuum is composed of scattered granules, and the sporozoites are vermiform with a refractile body and a nucleus. Isospora teresopoliensis n. sp. oöcysts are spherical to sub-spherical, 25.7 × 24.3 μm, with a smooth, bi-layered wall 1.3 μm thick. A micropyle, oöcyst residuum and polar granule are absent. Sporocysts are ovoid, 18.8 × 11.2 μm. The Stieda body is nipple-shaped and the substieda body is large and prominent. The sporocyst residuum is composed of scattered granules, and the sporozoites are large and elongate, with a refractile body and nucleus. Oöcysts of Isospora chanchaoi n. sp. are spherical to sub-spherical or ovoid, 24.2 × 22.0 μm, with a smooth, bi-layered wall c.1.2 μm thick. Both a micropyle and an oöcyst residuum are absent, but one or two polar granules are present. The sporocysts are ellipsoidal, 16.1 × 10.3 μm. The Stieda body is nipple-shaped and the substieda body is small but prominent. The sporocyst residuum forms a compact mass of granules, and the sporozoites are large and elongate, with a refractile body and a nucleus.     

Rice protein-body formation: all types are initiated by dilation of the endoplasmic reticulum

The ultrastructure of protein deposition in the starchy endosperm of developing rice (Oryza sativa L.) grains was examined in conventionally fixed (glutaraldehyde and osmium tetroxide) tissues and also in thick sections (0.3 m) of zinc iodide-osmium tetroxide post-fixed tissue. Three types of previously characterised protein body were observed and it was shown that each type was initiated by dilations of the endoplasmic reticulum. Crystalline type protein bodies were initiated by a ribosome-free dilation from rough cisternal endoplasmic reticulum and developed by inclusion of protein from dictyosome-derived vesicles. The large spherical and small spherical protein bodies developed within the cisternae of the rough endoplasmic reticulum.Abbreviations Cr crystalline protein body - DAF days after fertilization - ER endoplasmic reticulum - Ls large spherical protein body - Ss small spherical protein body - ZIO zinc iodide-osmium tetroxide     

Neuronal architecture of the central complex in Drosophila melanogaster

Summary On the basis of 1200 Golgi-impregnated brains the structure of the central complex of Drosophila melanogaster was analyzed at the cellular level. The four substructures of the central complex — the ellipsoid body, the fanshaped body, the noduli, and the protocerebral bridge — are composed of (a) columnar small-field elements linking different substructures or regions in the same substructure and (b) tangential large-field neurons forming strata perpendicular to the columns. At least some small-field neurons belong to isomorphic sets, which follow various regular projection patterns. Assuming that the blebs of a neuron are presynaptic and the spines are postsynaptic, the Golgi preparations indicate that small-field neurons projecting to the ventral bodies (accessory area) are the main output from the central complex and that its main input is through the large-field neurons. These in turn are presumed to receive input in various neuropils of the brain including the ventral bodies. Transmitters can be attributed immunocytochemically to some neuron types. For example, GABA is confined to the R1–R4 neurons of the ellipsoid body, whereas these cells are devoid of choline acetyltransferase-like immunore-activity. It is proposed that the central complex is an elaboration of the interhemispheric commissure serving the fast exchange of data between the two brain hemispheres in the control of behavioral activity.     

Fine structure of the unistellate sperm of the shrimp, Sicyonia ingentis (Natantia)

Sperm of the prawn Sicyonia ingentis were studied cytochemically and ultrastructurally. Striking cytological differences were noted between these natantian sperm and previously studied reptantian sperm. In general, the S. ingentis sperm are composed of a spherical main body that is partially encompassed by a morphologically diverse cap region, from which extends a single appendage or spike. The main body houses an uncondensed, Feulgen-positive nuclear region that is partially surrounded by a cytoplasmic band. A single layer of small, 600 Å, vesicles lines the periphery of the cytoplasmic band. Large membranous vesicles extend from the inner surface of the cytoplasmic band into the nuclear region. The nucleus is separated from the cap or acrosomal complex by a dense plate and a highly organized crystalline lattice, which is composed of geometric squares that are approximately 350 Å in dimension. The cap region also contains convoluted membrane pouches; a central granular core; spherical bodies; an electron-dense, saucer-shaped plate; and a large anterior granule. The convoluted membrane pouches and anterior granule are periodic acid-Schiff (PAS) positive. The anterior granule also demonstrates RNAase-stable red fluorescence with acridine orange staining. A spiralled spike, approximately 6 μm long, extends from the anterior end of the cap. The cap and spike are bound by a double membrane, which results from the fusion of the plasma membrane and the convoluted pouch membrane. The sperm's acrosome is thought to be composed of the two PAS-positive cap components and the spike.     

Light and Electron Microscopic Observations of Gametogenesis in Hastigerina pelagica (Foraminifera)*

SYNOPSIS. During gametogenesis mother individuals of Hastigerina pelagica (d'Orbigny) undergo significant morphological changes. Thirty h before gamete release, the cytoplasm changes from pale orange to bright red, possibly due to transport of stored lipids from the inner region to more peripheral parts of the cytoplasm. During the next 10 to 15 h the bubble capsule which surounds the calcareous shell is discarded. After all bubbles have disappeared, the individual sheds its spines by resorbing the spine bases close to the shell surface. A single mother nucleus divides into some hundreds of thousands of gamete nuclei within a span of ～ 20 h. A bulge of cytoplasm is extruded from the aperture and increases in size during the next 5 to 10 h. This bulge consists of cytoplasmic strands in which gametes and spherical bodies are embedded. The gametes and spherical bodies mature and are released during the afternoon and early evening. The gametes have 2 unequal acronematic flagella. A previously undescribed structure in foraminiferal reproduction is the spherical body which consists of a large vacuole surrounded by a thin cytoplasmic layer in which several nuclei, various typical cell organelles and multiple flagella are present. The spherical bodies are believed to play a role as receptacles of waste material, possibly including residual digestive enzymes, thereby protecting the gametes from lysis during the reproductive process. Fusion of gametes and further development into the next generation have not been observed.     

CYTOLOGY OF BLUE-GREEN ALGAE. I. THE CELLS OF SYMPLOCA MUSCORUM

Pankratz , H. S., and C. C. Bowen . (Iowa State U., Ames.) Cytology of blue-green algae. I. The cells of Symploca muscorum . Amer. Jour. Bot. 50(4): 387–399. Illus. 1963.—The cellular morphology of Symploca muscorum is described, based upon electron micrographs utilizing improved techniques of specimen preparation. Except for a limiting plasma membrane, ribosomes, and Feulgen-positive chromatin, the cells have little resemblance to those of higher organisms. The longitudinal components of the cellular envelope consist of a 200–300 mμ fibrous sheath and a complex inner investment about 35 mμ thick which includes at least 3 distinctly layered wall elements in addition to the typical 7-mμ unit membrane forming the plasma membrane. A row of very small elongate “pores” pierce the inner investment on each side of, and immediately adjacent to, the junction of the longitudinal walls and the crosswalls. Crosswalls vary in thickness from 3 to 20 mμ, depending upon their age, and arise as elaborations of the inner layers of the longitudinal inner investment. The photosynthetic lamellar component of the cytoplasm consists of flattened sacs formed from unit membranes. The lamellae are concentrated in the peripheral region of the cell and usually are parallel to the longitudinal wall. These often extend from one crosswall to the next but, except for a few cases, are not continuous with the plasma membrane at either end. The Feulgen-positive nucleoplasm appears as an anastomosing system of lightstaining regions containing fibrils 2–5 mμ in diameter. The morphology and interrelationship of a number of other cellular elements are described: (1) structured granules range up to 0.5μ in diameter and occur near crosswalls; (2) polyhedral bodies, 0.2–0.5μ in diameter, are closely associated with the nucleoplasm; (3) “cylindrical bodies” characteristically consist of 2 concentric cylinders, are about 13 mμ in diameter and up to lμ in length; (4) “α granules” are spherical or somewhat elongate elements about 30 mμ in diameter and characteristically associated with the photosynthetic lamellae and structured granules; (5) “β granules” are spherical, highly osmiophilic granules which range from 30 to 90 mμ in diameter; (6) ribosomes, 10–15 mμ, in diameter, are most numerous near the nucleoplasm; (7) plasmodesms penetrate the crosswalls between adjacent cells. The cells of this organism can best be described as being in a “steady state” of division, and there is no evidence of any kind of organized distribution of the nucleoplasm to daughter cells during the constant progress of cytokinesis.     

Electron Microscopy of the Spherical Body of Oral Spirochetes In Vitro: Further Studies

The surface and inner structure of the spherical bodies (SB) produced by the human oral treponeme strain G7201, similar to Treponema macrodentium, were studied by electron microscopy. Ultrathin sectioning and scanning techniques demonstrated that in the presence of a high concentration of sucrose, the outer envelope of one or both terminal ends of this oral spirochete changed into a swollen structure, the SB. Spirochetal cells adhered firmly to the surface of the resultant body. The membrane of the SB, i.e. the outer envelope, enclosed the coiled protoplasmic cylinder and five axial fibrils which were located between the envelope and the cylinder. Large expanded protoplasmic cylinders were observed, surrounded by a partially disrupted double membrane in some SBs. A number of frizzly fibrous structures, which differed from axial fibrils in number and shape, were also observed within these SBs. Except for abnormal or partially broken cylinders, the protoplasmic cylinders tended to be located close to the inner surface of the SB membrane, resulting in a central vacant space with occasional axial fibrils. These findings suggest that the oral spirochete produces an SB by terminal expansion of the outer envelope in the presence of high concentrations of sucrose. The outer envelope of the SB, which consists of two electron-dense layers, has the property of binding spirochetal cells to its outer layer and the protoplasmic cylinder and axial fibrils to the inner layer. Some protoplasmic cylinders were also observed to be swollen in the presence of high sucrose concentrations.     

Exogenous Stages of Isospora serini (Aragão) and Isospora canaria sp. n. in the canary (serinus canarius Linnaeus)*

Exogenous stages of Isospora serini (Aragão) and Isospora canaria sp. n. from the canary (Serinus canarius Linnaeus) are described. Oocysts of I. serini are spheroid and average 19.2 × 20.1 μ m, while those of I. canaria are larger, more ellipsoid, and average 21.8 × 24.6 μ m. No oocyst residuum is present and the oocyst walls of both species are colorless, transparent, and single layered. Sporocysts average 9.4 × 15.2 μ m for I. serini and 11.5 × 18.1 μ m for I. canaria. The I. canaria sporocyst has a substiedal body, but none was found in I. serini sporocysts. Both species have a spherical sporocyst residuum; this was obscured in the I. serini sporocyst by scattered granules. Living sporozoites of I. canaria average 3.6 × 16.9 μ m and have 1 to 3 refractile globules; those of I. serini have 2 globules and average 2.8 × 12.6 μ m. A disseminated infection of the mononuclear phagocytes results from administration of I. serini while I. canaria oocysts give rise to a typical coccidian infection restricted to the intestinal epithelium. Asexual stages of I. serini in macrophages are indistinguishable from parasites previously called avian Toxoplasma, Atoxoplasma, and Lankesterella.     

Factors affecting gene delivery by particle bombardment ofDendrobium orchids

Summary Five parameters were examined for their effect on transformation ofDendrobium tissues by microprojectile bombardment. The superpromoter in pBI426 produced at least 1.5 times as many transient transformants as the single cauliflower mosaic virus 35S promoter in pBI121 (37 to 69% vs. 0 to 44%) with dark and frequent GUS (β-glucuronidase) staining. Tissue, genotype, and type of microparticle significantly affected transient GUS activity. Higher expression was seen in protocormlike bodies and in hybrid UH44 compared to etiolated shoots and protocorms and to hybrids M61 and K1329-39. Microparticles of 1.6-μm Bio-Rad gold were more effective than 1.0-μm ASI gold. Transient GUS activity did not differ among protocormlike bodies bombarded using helium propellant pressures of 650, 900, or 1100 psi. Transgenic plants were recovered fromDendrobium UH800 protocormlike bodies bombarded with pBI426-coated, 1.1-μm tungsten particles using an early-model gunpowder-driven apparatus with an estimated stable transformation rate of 11.7%. One transgenic plant ofDendrobium UH44 was recovered from etiolated shoot explants bombarded with pBI121-coated, 1.1-μm tungsten particles using the Dupont PDS-1000 with a stable transformation rate of 0.17%. Positive selection results showed 100 to 200 mg·liter⁻¹ kanamycin to be appropriate for regeneration of transgenic plants from protocormlike bodies, protocorms, and etiolated shoot explants over a 3- to 9.5-mo. period.     

CHARACTERIZATION OF VACUOLAR BODIES IN SPARTINA ALTERNIFLORA: I. FORMATION,DEVELOPMENT, MORPHOLOGY,AND ULTRASTRUCTURE

Spherical, golden bodies, 0.5 to 25 μm in diameter, were noted in outer bundle sheath and mesophyll of cells of fresh sections of Spartina alterniflora leaves. Attempts to further characterize these structures with light and electron microscope (EM) techniques after dehydration failed initially because these bodies were soluble in organic solvents such as alcohol. Subsequently, it was found that certain heavy metals would stabilize the structure so that dehydration techniques could be used. The resultant stabilized bodies as viewed with EM were found to reside in the cell vacuole. Two major structural components were recognized: (1) a granular matrix and (2) a non-electron dense internal vesicle. Internal vesicles were not always present. No membranes were visible with this technique. These vacuolar bodies also were found to occur in parenchyma cells of roots, peduncles, glumes, and rhizomes of S. alterniflora. The material which forms the vacuolar body matrix is probably produced in the cytoplasm and gradually accumulates in the vacuole, forming larger and more numerous vacuolar bodies during the growing season. The matrix material remains in the leaf cells following their senescence.     

Ultrastructure of grey mullet (Mugil cephalus,Linnaeus, 1758) spermatozoa as revealed from light,scanning and transmission electron microscopy

Spermatozoa morphology and fine structure were studied in the grey mullet, Mugil cephalus using light, scanning and transmission electron microscopy. Light microscopy observations indicate a semi‐cystic type of spermatogenesis in the testis. The electron microscopy micrograph showed that the spermatozoon of M. cephalus is uniflagellated (total length 5.78 ± 1.26 μm), differentiated into an ovoid‐shaped head without acrosome (1.80 ± 0.35 μm in length and 1.91 ± 0.30 μm in diameter), with a short midpiece and a long cylindrical flagellar tail (length 3.60 ± 0.50 μm). The midpiece is characterized by the presence of four to five vacuoles, a cytoplasmic canal, two centriole and two spherical mitochondria having a flat type of cristae. Chromatin granules of the nucleus form an electron‐dense homogeneous mass. The flagellum consists of nine peripheral microtubules and a central pair (9 + 2) surrounded by the plasma membrane with side fins. The results confirm that spermatozoa of M. cephalus are perciform or teleostean type II. Information generated from the present study will be useful in taxonomic classification, cryopreservation and breeding work.     

Sperm ultrastructure in two species of the polychaete genusHarmothoe (Polynoidae)

The structure of spermatozoa is described for two species of polynoid polychaete,Harmothoe imbricata andHarmothoe impar, from material fixed and examined by both scanning and transmission electron microscopy. The two species undergo spermiogenesis within discrete testes. The testis ofH. imbricata is shown to have a layer of epithelial cells which possess an outer cuticular layer and a microvillous inner surface. Spermatocytes of both species are spherical but there are marked differences in the shape and size of the spermatozoa of the two species.H. impar has a classical primitive spermatozoon with a rounded head (2 μm long) and a button-shaped acrosome. Fully differentiated spermatozoa ofH. imbricata are modified from the primitive form by having a long head (10 μm length) with a pointed acrosome about 6 μm in length. Spermatozoa ofH. imbricata have a ring of up to fourteen mitochondria around a centrally inserted flagellum at the posterior whereasH. impar has a ring of four or five spherical mitochondria. Spermiogenesis is well synchronised inH. imbricata but all developmental stages can be found simultaneously in the testis ofH. impar. The differences in sperm structure of the two species may be related to differences in breeding biology which are hitherto unknown.