PRIMORDIAL GERM-CELLS AND OOCYTES OF BRANCHIOSTOMA-VIRGINIAE (CEPHALOCHORDATA, ACRANIA) ARE FLAGELLATED EPITHELIAL-CELLS - RELATIONSHIP BETWEEN EPITHELIAL AND PRIMARY EGG POLARITY

Primordial germ cells (PGCs) are described from the gonad of c. 2 cm j uvenile Branchiostoma virginiae; early oocytes (c. 10 mu m) and enlarg ing, previtellogenic oocytes (c. 35 mu m) are described from the ovary of c. 5 cm adults. The germinal epithelium of the juvenile gonad and adult ovary is composed of both germinal and somatic cells. In the juv enile, somatic cells retain contact with the basal lamina of the germi nal epithelium though their perikarya may be displaced towards the lum en; the germinal epithelium is, therefore, a simple but pseudostratifi ed epithelium. In the adult ovary, somatic cells may lose contact with the basal lamina and the epithelium appears to become stratified. PGC s and oocytes are identified as germ cells by the presence of nuage. P GCs and oocytes are polarised epithelial cells. They rest on a basal l amina, extend apically towards a lumen, form adhering junctions with n eighbouring cells, and exhibit apical-basal polarity. PGCs and early o ocytes have an apical flagellum with an associated basal body, accesso ry centriole, and one or II-tore striated rootlet fibres. The flagellu m is surrounded by a collar of microvilli. Once oocytes begin to enlar ge and bulge basally into the connective tissue layer, the flagellum i s lost, but the basal bodies and ciliary rootlets are present at the a pex of 35 mu m oocytes. Similarities of the oogenic pattern in cephalo chordates and echinoderms indicate that the establishment of egg polar ity in deuterostomes is influenced by the polarity of the germinal epi thelium.