Sarcocystis mephitisi n. sp. (Protozoa: Sarcocystidae), Sarcocystis neurona-like and Toxoplasma-like infections in striped skunks (Mephitis mephitis)

Two structurally distinct types (A, B) of microscopic sarcocysts were found in muscles of 4 of 5 feral skunks. Type A sarcocysts had sarcocyst walls of up to 6 microm thick. The villar protrusions (Vp) on the sarcocyst wall were up to 5 microm long. The Vp were constricted at the base, expanded in the middle, and had a blunt tip. Numerous microtubules were present in the Vp and in the granular layer. Bradyzoites were up to 11 microm long and up to 3.2 microm wide. Based on the distinctiveness of the Vp, a new name, Sarcocystis mephitisi is proposed for type A sarcocysts. Type B sarcocysts had a relatively thin (approximately 1-2 microm thick) sarcocyst wall and the Vp were slender and tapered toward the tip. These sarcocysts were structurally similar to S. neurona sarcocysts. A Toxoplasma gondii-like tissue cyst was found in a section of tongue of 1 of the 4 skunks.     

Structure of Sarcocystis neurona sarcocysts.

The ultrastructure of Sarcocystis neurona sarcocysts was studied from muscle of an experimentally infected cat. The cat was killed 144 days after being fed sporocysts from a naturally infected opossum. Sarcocysts were microscopic, up to 700 microm long, and up to 50 microm wide. By light microscopy, the sarcocyst wall was 1-2 microm thick. Ultrastructurally, the sarcocyst wall consisted of numerous villar protrusions. The villar protrusions were up to 2.8 microm long and 0.4 microm wide, with a tapered end. Microtubules extended from the tip of the villus to the base and occasionally extended deep into the granular layer. The granular layer was approximately 0.5 microm thick. Longitudinally cut bradyzoites were 5.2 by 1.2 (4.8-6.5 by 1.0-1.3) microm in size. Micronemes in bradyzoites were numerous and located in the anterior 1/3 of the conoidal end.     

A new species of Sarcocystis (Apicomplexa: Sarcocystidae) from the black bear (Ursus americanus)

Infection with Sarcocystis species is common in herbivores but is rare in bears. Histological sections of 374 black bears (Ursus americanus) from Pennsylvania were examined for sarcocysts. In total, 3 sarcocysts were found in 3 bears, with 1 sarcocyst per section. Sarcocysts from 2 bears were considered a new species, Sarcocystis ursusi. Sarcocysts of S. ursusi n. sp. were microscopic and contained only bradyzoites. By light microscopy, the sarcocyst wall was thin (< 0.5 microm thick) and had minute serrations. Ultrastructurally, the serrations on the sarcocyst wall consisted of villar protrusions (Vp) that were mostly 0.5 microm long. The Vp had bundles of electron-dense microtubules that were as wide as long; these microtubules extended deep into the ground substance layer, a feature that distinguished this species from unnamed sarcocysts from black bear. Bradyzoites were 4.8-6.0 microm long. The sarcocyst from the third bear was structurally different from S. ursusi; its sarcocyst wall was approximately 2 microm thick and had finger-like villi on the cyst wall giving the sarcocyst wall a striated appearance.     

Ultrastructural studies of Sarcocystis cruzi (Hasselmann, 1926) Wenyon, 1926 infection in cattle (Bos taurus): Philippine cases

This paper documents the first report of Sarcocysti s cruzi infection in domesticated cattle (Bos taurus) in the Philippines. Fusiform-shaped microscopic sarcocysts (183-578 microns long and 20-98 microns wide) with distinct septae were found in the skeletal, striated and heart muscle. The sarcocyst wall or parasitophorous vacuolar membrane, 1.37-2.75 microns thick consisted of closely-packed villar protrusions 80-400 nm in dm. Middle and distal segments of VP were bent approximately 90 degrees parallel to the cyst wall surface. The villar core lacked microtubules, and at some points, the distal ends of the VP collectively formed conical tufts. Primary cyst wall had numerous 70-100 nm bubble-like undulations, and the ground substance was 0.25-0.5 micron in thickness. The ultrastructure of S. cruzi cyst wall typifies the Type 7 sarcocyst wall, and bears close similarities with the Philippine and the Vietnam strain of bubaline Sarcocystis levinei.     

Cytoskeleton-induced alterations of the lectin activity in winter wheat under cold hardening and abscisic acid (ABA)

The roots and leaves of 7-day seedlings of three winter wheat cultivars differing in frost resistant were used to study changes in lectin activity under cytoskeleton modifiers (DMSO-7%; colchicine-1 m m; oryzalin-15 microm; cytochalasin B-15 microm) of non-hardened (23 degrees C) and hardened (2-3 degrees C, 3-7 day) plants. Plants were grown with ABA (30 microm) or without ABA. Pretreatment with colchicine, oryzalin [inhibitors of microtubules (MT) polymerization], cytochalasin B [inhibitor of microfilament (MF) polymerization] increased the activity of cell wall lectins, although pretreatment with DMSO (stabilizer of microtubules) decreased the activity. Both hardening and ABA decreased the effect of the cytoskeletal modifiers. These results could be explained by the appearance of tolerant MTs with less affinity. It is probable that increase in the activity of cell wall lectins may be the compensatory mechanism which stabilizes the cytoskeleton structure in conditions tending to disrupt it. The genotype with low resistance had higher sensitivity of lectin activity to cytoskeleton modifiers than the frost resistant genotype. The results suggest that leaves have more stable MTs and MFs and stronger MT-MF binding than roots.     

Three new species of Isospora schneider, 1881 (Apicomplexa: Eimeriidae) from the double-collared seed eater, Sporophila caerulescens (Passeriformes: Emberizidae), from Eastern Brazil

Three isosporan species are described from the double-collared seedeater, Sporophila caerulescens from Eastern Brazil. Isospora sporophilae n. sp. oocysts spherical to subspherical; oocyst wall bi-layered, smooth, inner layer colorless to pale yellowish, 21.6 x 20.9 (19.20-23.20 x 18.40-22.60) microm, shape-index 1.03 +/- 0.02 (1-1.10), with no micropyle or oocyst residuum. Polar bodies splinter-like or comma-like. Sporocysts ovoidal, 15.2 x 10.6 (17.40-12.80 x 12.60-8.40) microm, shape-index 1.43 +/- 0.14 (1.17-1.81), with knob-like Stieda body and residuum. Large crystalloid body in the center of the sporocyst. Isospora flausinoi n. sp. oocysts spherical to subspherical, oocyst wall bi-layered, smooth, colorless, 17.30 x 16.53 (14-20 x 13.60-20) microm, shape-index 1.05 +/- 0.04 (1-1.21). Micropyle and oocyst residuum absent; presence of a large polar body. Sporocystpiriform, 14.88 x 10.70 (11.80-18 x 8-12.40) microm, shape-index 1.40 +/- 0.18 (1.07-1.77), with smooth, thin, single-layered wall. Sporocyst with rounded Stieda body with no substieda body, and residuum composed of granular material. Isospora teixeirafilhoi n. sp. oocysts spherical to subspherical, oocyst wall bi-layered, smooth, colorless, 17.41 x 16.81 (15.60 - 19.40 x 14.20-18.80) microm. Shape-index 1.04 +/- 0.08 (1-1.12). Micropyle and oocyst residuum absent; presence of a small double-lobuled polar body. Sporocyst ovoid, 11.74 x 8.12 (9-14.20 x 6.20-9.40) microm. Shape-index 1.46 +/- 0.23 (1.06-1.88). Sporocyst with knob-like Stieda body, no sub-Stieda body and residuum composed of granular material.     

Ultrastructure of spermatozoa of tench Tinca tinca observed by means of scanning and transmission electron microscopy

Structure of tench (Tinca tinca L.) spermatozoa was investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Spermatozoa of 26.1+/-3.8 microm total length possessed typical primitive simple structure, called "aqua sperm", without acrosomal head structures. It was probably the smallest spermatozoon described among cyprinid fishes. Heads were mostly composed of dense and slightly granular material, which appeared to be fairly homogeneous except for the occasional appearance of vacuoles. The midpiece remained separated from the flagellum by the cytoplasmic channel; it was cylindric/cone-shaped, 0.86+/-0.27 microm in length and 1.17+/-0.24 microm in width at proximal part. The proximal centriole was located in the "implantation fossa". The distal centriole appeared almost tangential to the nucleus and it functioned as a basal body for the flagellum. It had an orientation of 140 degrees with respect to the distal centriole. The sperm flagellum with 25.45+/-2.47 microm of total length had no any fin. The diameter of the flagellum perpendicular to the plane of the doublet of central microtubules was 173.67+/-20.45 nm and horizontal plane of the central microtubules was 200.71+/-20.45 nm. Peripheral doublets and the central doublet of microtubules measured 23.39+/-3.18 and 35.88+/-4.44 nm in width, respectively. The diameter of a microtubule was only 9.14+/-2.97 nm. A vesicle was attached to the most basal region of the flagellum and located just under plasma membrane of the flagellum.     

Ultrastructure of Frenkelia sp. from a Norwegian lemming in Finland

An apparently healthy Norwegian lemming (Lemmus lemmus) caught in northern Finland was observed to have a whitish body 0.5 to 1.0 mm in diameter in the external layer of the cerebral cortex. By light microscopy a highly lobulated cyst of Frenkelia sp. was observed. By transmission electron microscopy lemmus) collected in the cyst wall was seen consisting of a parasitophorous vacuolar membrane, an underlying electron-dense layer and a granular layer. The membrane was only slightly convoluted. The protrusions of the cyst wall appeared round but were often not distinctive. A very thin septum divided the interior of the cyst into compartments packed with bradyzoites and maturing zoites. The bradyzoites were elongate measuring 5-8 x 1.5-2 microm. This is the first electron microscopical study of Frenkelia sp. from L. lemmus.     

Eimeria pavoaegyptica sp. nov. (Apicomplexa: Eimeriidae) in faeces of Indian peacocks, Pavo cristatus Linnaeus, 1758 (Galliformes: Phasianidae) from Egypt

Coprological examination of 15 Indian peacocks, Pavo cristatus, revealed the presence of a coccidium species of the genus Eimeria, which apparently represents a previously undescribed species. Sporulation is exogenous and fully developed oocysts of Eimeria pavoaegyptica sp. nov. are ellipsoidal, with a dimension of 15 (13-16) × 12 (10-12.9) microm and with a shape index of 1.25 (1-1.3). The sporulated oocysts have no micropyle but enclose one large rectangular-shaped polar granule and an oocyst residuum. The oocysts have a distinct two-layered wall, which is ~approximately1.7 microm thick. The outer layer has a smooth texture; it fills ~? of the total thickness and appears bicolored. The sporocysts are boat-shaped, of about 10 (9-11) × 4 (4-4.7) microm; their average shape-index is 2.5 microm with a small pointed Stieda body and a smooth, thin single-layered wall. No substieda body is detected. The sporocysts contain numerous, nearly uniform granular residua. The sporozoites are banana-shaped, 6 × 3 microm and each has two different-sized refractile bodies.     

The fine structure of the phoront of Gymnodinioides pacifica, a ciliated protozoan (Ciliophora, Apostomatida) from euphausiids of the Northeastern Pacific

Phoretic stages of the exuviotrophic apostome Gymnodinioides pacifica were examined using transmission and scanning electron microscopy (TEM and SEM). TEM revealed that the mature cyst wall possesses 2 or 3 layers differing by the presence or absence of the third inner layer. This inner layer may represent a different form of the middle wall material. The inner cyst layer is approximately 0.15 microm thick and has striations with a periodicity of approximately 19 nm. The middle cyst layer has a variable thickness and the outer dense layer is approximately 0.1 microm thick. The 3 layered cyst wall had a thickness of 0.3-0.7 microm and averaged 0.5 microm. Advanced phoront stages were enclosed by fully formed cyst walls or by cyst walls thinned to approximately 0.1 microm, as the phoronts prepared to excyst prior to host ecdysis. Additionally, we report the fine structure of the rosette, trichocysts, nuclei, food plaquettes, oral fiber, and other cytoplasmic inclusions. SEM revealed an outer cyst wall layer connected to the secreted peduncle material, which was observed to extend over a wide (15 microm) area on the host setae. Cysts were usually attached at their posterior ends or, less frequently, along their side.     

Location of DNA-binding proteins and disulfide-linked proteins in vaccinia virus structural elements.

Treatment with sodium dodecyl sulfate (SDS) converted the vaccinia virus strain IHD-J into particles of two types: (i) ghosts which possessed a thin-membrane vesicle derived from basement part of the virus membrane with attached lateral bodies and a membranous structure derived from the core wall and (ii) aggregates of a DNA-nucleoprotein eluted from the core. These particles lacked lipids, and all the viral phospholipids were detected in the SDS-soluble fraction. The viral membrane was composed of an SDS-soluble coat layer and the basement membrane, and the basement membrane was maintained by a mechanism other than the lipid bilayer. By comparisons of protein species in morphologically distinct subviral particles prepared by several solubilizing methods, protein compositions of viral structural elements were suggested as follows: 25,000-molecular-weight viral protein-17,000-molecular-weight viral protein ( VP25K - VP17K ), viral basement membrane; VP13 . 8K , major component of the lateral body; VP70K , VP69K , VP66K , and VP64K , minor components of the lateral body; VP61K , outer layer of core wall; VP57K - VP22K , inner layer of core wall; and VP27K - VP13K , nucleoprotein. These structural elements found in the SDS-insoluble particles dissolved in the same SDS solution under reducing conditions, indicating that the disulfide linkages seem to have a principal role in maintaining their morphological integrity. VP57K , VP27K , VP13 . 8K , and VP13K were revealed to possess affinity for DNA. Denatured calf thymus DNA and viral DNA in double- or single-stranded form associated equally well with these proteins, but RNA did not bind. Therefore, it was strongly suggested that disulfide-linked VP27K - VP13K represented the nucleoproteins of vaccinia virus. A structural model of vaccinia virus is proposed and discussed.     

Theoretical and experimental study towards a nanogap dielectric biosensor

Theoretical and experimental studies of nanogap capacitors as potential label free biosensors are presented. The nanogap device is capable of detecting the existence of single stranded DNA (ssDNA) oligonucleotides (20-mer) in 100 nM aqueous solutions using a 20 nm gap of 1.2 pl in volume. While the dielectric properties of DNA solution have been widely investigated, early approaches are limited at low frequency by the parasitic noise due to the electrical double layer (EDL) impedance. Nanogap electrodes have the potential to serve as biomolecular junctions because their size (5-100 nm) minimizes electrode polarization effects regardless of frequency. In this paper, we modeled the effects of the EDL interaction between two parallel nanogap electrodes by solving the Poisson-Boltzmann (PB) equation for equilibrium state. When the gap size is smaller than the EDL thickness, the dependence of the nanogap capacitance on the ionic strength is insignificant. This is critical in using the capacitance change as an indicator of the existence of target molecules. The predicted capacitance of nanogaps filled with various ionic strength electrolytes was in quantitative agreement with the experimental measurements. The various concentrations of the target molecules in nanogap sensor were characterized. A capacitance change of a 20 nm x (10)1.5 microm x 4mm gap from 3.5 to 4.1 nF at 200 Hz was recorded between deionized water (DI) and 100 nM ssDNA solution (about 70,000 molecules inside the gap for equilibrium state).     

Eimeria hajeki n. sp. (Apicomplexa: Eimeriidae), a new coccidian parasite of the pygmy chameleon, Rampholeon temporalis (Matschie, 1892) (Reptilia: Chamaeleonidae) from Usambara Mountains, Tanzania.

Fecal samples from 10 pygmy chameleons, Rampholeon temporalis (Matschie, 1892), an endemic species of the Usambara Mountains in northeastern Tanzania, were examined for coccidian parasites. Two (20%) chameleons were found to be passing oocysts of Eimerio Schneider. Comparison with other species of Eimeria indicates that the coccidian found represents a new species. Sporulated oocysts of Eimeria hajeki n. sp. are oval, 30.2 (29-31) by 23.5 (22-25) microm, with a shape index (length/width) of 1.3 (1.2-1.4) and a 2-microm-thick rough, bilayered wall. Micropyle and polar granule are absent. Sporocysts are oval to rhomboidal, 10.8 (9-11.5) by 8.8 (7.5-10) microm, with a shape index of 1.2 (1.15-1.3) and a wall composed of 2 valves joined by a suture.     

Eimeria from bats of Bolivia: two new species from vespertilionid bats.

Between 1985 and 1987, fecal samples were collected from 71 bats representing 14 species (Desmodontidae, Molossidae, Noctilionidae, Phyllostomidae, Vespertilionidae) from 8 localities in 3 states (Beni, Pando, Santa Cruz) in Bolivia, South America. Of these, 2 black myotid bats (Vespertilionidae), Myotis nigricans, and 1 tent-making bat (Phyllostomidae), Uroderma magnirostrum, had oocysts in their feces that represent undescribed species of Eimeria. The new species from M. nigricans (2/4, 50%) has sporulated oocysts that are subspheroidal, 18.9 x 16.9 (17-23 x 14-20) microm, without a micropyle; oocyst residuum of 6-8 spheroidal globules and 1 highly refractile polar granule are present. The oocyst wall has 2 layers (approximately 1.3 microm thick), with a rough outer layer. Ovoidal sporocysts are 10.1 x 7.4 (7-14 x 5-10) microm, with a Stieda body, substieda body, and a sporocyst residuum. The new eimerian species from U. magnirostrum (1/2, 50%) has sporulated oocysts that are subspheroidal to ellipsoidal, 23.8 x 20.8 (20-26 x 19-24) microm, without micropyle or oocyst residuum, but 1-3 polar granules are present. The oocyst wall has 2 layers (approximately 1.5 microm thick), with a rough, mammilated outer layer. Ovoidal sporocysts are 11.6 x 8.6 (10-12 x 7-10) microm, with a Stieda body, substieda body and a sporocyst residuum.     

Two new species of coccidia (apicomplexa: Eimeriidae) from the bearded false chameleon Chamaeleolis barbatus (Sauria: polychridae) from cinco pesos, Pinar Del Río, Cuba.

Parasitological examination of bearded false chameleons Chamaeleolis barbatus freshly imported from Cuba revealed the presence of 2 species of coccidia that are described as new. Oocysts of Isospora chamaeleolidis n. sp. are spherical to slightly subspherical, 16.1 (13-21) x 15.6 (13-19) microm, with a brownish and bilayered wall approximately 1.0-1.5 microm thick; outer layer markedly pitted. 0.75-1.0 microm thick. One, rarely 2, globular polar granules, 1.5 in diameter are present in the sporulated oocysts. Sporocysts are ellipsoidal, 10.8 (10-13) x 7.8 (7-9) microm, with a smooth, colorless, and unilayered sporocyst wall. Stieda body and substieda bodies are present. A sporocyst residuum is present, consisting of small granules of irregular size scattered among the sporozoites. Oocysts of Eimeria chamaeleolidisbarbati n. sp. are broadly oval, 19.0 (17-21) x 15.7 (15-17) microm, with a bilayered, colorless oocyst wall approximately 0.75 thick; outer layer of oocyst wall is smooth, 0.5 microm thick. One or 2, rarely 4, globular, irregular polar granules, approximately 1.5 microm in diameter, are present in sporulated oocysts. Sporocysts are broadly oval, 7.4 (7-8.5) x 6.1 (5.5-7) microm, with a smooth, colorless, and unilayered sporocyst wall, composed of 2 valves joined by suture; Stieda body and substieda bodies are absent.     

Dietary antioxidant curcumin inhibits microtubule assembly through tubulin binding

Curcumin, a component of turmeric, has potent antitumor activity against several tumor types. However, its molecular target and mechanism of antiproliferative activity are not clear. Here, we identified curcumin as a novel antimicrotubule agent. We have examined the effects of curcumin on cellular microtubules and on reconstituted microtubules in vitro. Curcumin inhibited HeLa and MCF-7 cell proliferation in a concentration-dependent manner with IC(50) of 13.8 +/- 0.7 microm and 12 +/- 0.6 microm, respectively. At higher inhibitory concentrations (> 10 microm), curcumin induced significant depolymerization of interphase microtubules and mitotic spindle microtubules of HeLa and MCF-7 cells. However, at low inhibitory concentrations there were minimal effects on cellular microtubules. It disrupted microtubule assembly in vitro, reduced GTPase activity, and induced tubulin aggregation. Curcumin bound to tubulin at a single site with a dissociation constant of 2.4 +/- 0.4 microm and the binding of curcumin to tubulin induced conformational changes in tubulin. Colchicine and podophyllotoxin partly inhibited the binding of curcumin to tubulin, while vinblastine had no effect on the curcumin-tubulin interactions. The data together suggested that curcumin may inhibit cancer cells proliferation by perturbing microtubule assembly dynamics and may be used to develop efficacious curcumin analogues for cancer chemotherapy.     

Interphase microtubules in cultured cells: long or short?

Presently, the question about the length of microtubules in the interphase cell became actual, since the parameters of dynamic instability of the plus end measured in vivo do not allow one to explain the rapid turnover of the long microtubule system. The problem may be solved if one of the following suppositions is assumed: either microtubules undergo rapid depolymerization from the minus end or they are on the average much shorter than it is usually considered. To check the last hypothesis, we have reconstructed microtubules using stereophotography of electron microscopic sections. Microtubules around the cell center in cultures of epithelial cells (kidney of pig embryo (PK) and bovine trachea (FBT)) and fibroblasts (MEF, primary mouse embryo fibroblasts, and L cells), as well as at the periphery of PK cells were studied. All in all, no less than 200 microtubules were found near the centrosome in each cell culture. From 2.5 to 8% microtubules were beyond the studied volume (4.0 x 5.5 x 1.5 microm). Most of microtubules in all studied cell lines were up to 1 microm and about 1/3 of them were 0.2-0.4 microm long. The mean length of microtubules surrounding the centrosome in different cell lines differed insignificantly and equalled 0.4-0.8 microm. In this case, the microtubules attached to the centrosome were on the average slightly shorter than the free ones. Thus, almost all microtubules around the centrosome are short, and the majority of those attached to it do not reach the cell periphery. A similar reconstruction of a part of the PK cell cytoplasm (10 x 35 microm) has shown that at the periphery, the mean length of microtubules is about 1.6 microm and most of them are 0.5 to 1.5 microm long. Thus, our data confirm the recent hypothesis of Vorobjev et al. (I. A. Vorobjev, T. M. Svitkina, and G. G. Borisy, J. Cell Sci. 110:2635-2645 (1997)) that most of microtubules in the cells are not connected with the centrosomes.     

Eimeria curvata n. sp.(Apicomplexa: Eimeriidae) in Columbina talpacoti and Scardafella squammata (Aves: Columbidae) from Brazil

Eimeria curvata is a new coccidian described in the doves Columbina talpacoti and Scardafella squammata from western of the State of S?o Paulo, Brazil. The oocysts are ovoid to ellipsoid, 18.3 (17-19) microm x 15.5 (15-17) microm, with a shape index of 1.2 (1.1-1.3). The wall is colorless, smooth and double-layered. A polar granule is present, but there is no micropyle or oocyst residuum. The sporocysts are elongate, 12.3 (11.5-13) microm x 5.8 (5.5-6) microm with a curved anterior portion and a smooth, thin, single-layered wall. The Stieda body is protuberant and nipple-like; there is no substieda body. The sporozoites lie head-to-tail in the sporocyst and contain a large refractile body at the extremities. The sporocyst residuum contains small granules uniformly distributed in the middle of the sporocyst. The prevalence of E. curvata n. sp. was 17.4% and 12.8% in C. talpacoti and S. squammata, respectively.     

Clinical muscular sarcocystosis in a dog

Muscular sarcocystosis is a rare infection in dogs. Clinical myositis associated with an unidentified species of Sarcocystis was diagnosed in an adult dog from Canada. There was granulomatous myositis associated with numerous immature sarcocysts in a muscle biopsy obtained from the dog. The sarcocysts were up to 550 microm long and up to 45 microm wide. The sarcocyst wall was approximately 1 microm thick and contained short, stubby, villar protrusions that lacked microtubules. This is the first report on clinical muscular sarcocystosis in a dog.     

Fine structure of swarmers of Cladophora and Chaetomorpha

Summary Naked swarmers of Cladophora have been collected and wall synthesis and development have been followed using the techniques of freeze-etching and sectioning. Swarmers frozen after 9 hours liberation have lost their flagella, developed the characteristic fibrous layer and show the initial stages of wall production. Both the first formed (randomly oriented) and the later (more ordered) microfibrils appear to have a distinct granular texture. Occasionally linear arrays of granules up to 4 m long may be seen. After 5 days settling a thick wall composed of almost transversely oriented microfibrils is present and a rhizoid is pushed out. Also characteristic of this stage is the central localisation of cell components and peripheral vacuolar distribution. Longitudinally oriented microtubules also reappear at this stage having been absent during carlier wall formation.A possible relationship between the cortical microtubules of the motile swarmer and the development of the fibrous layer is suggested.