STRUCTURE OF THE TESTIS AND CHANGES SHOWN DURING THE ANNUAL REPRODUCTIVE-CYCLE IN CUCUMARIA-JAPONICA (ECHINODERMATA, HOLOTHUROIDEA)

In the holothurian, Cucumaria japonica, deep invaginations of the germ inal epithelium of the testis are formed during the period of active s permatogenesis (January-February) but are reduced in prespawning anima ls (August). The invaginations contain basal lamina which envelope the testis and separate the haemal sinus from the gonad lumen. They are l ined with germinal epithelium. Nurse cells are not present within regi ons of the germinal epithelium associated with invaginations of the la mina. These regions are invested by spermatogenic cells only.