A cytochemical study of oocyte growth in four species of Millipedes.

Abstract

The cytochemistry of oocyte growth was investigated in four species of millipedes; Narceus americanus, Oxidus gracilis, Cheiropus plancus, and a Pleuroloma species, probably P. cala. The oocyte of all four species produced a yolk nucleus which arose in contact with the nuclear membrane, subsequently detached, migrated into the central ooplasm and disrupted coincident with the appearance of protein yolk granules in the oocyte cytoplasm. Since the follicular epithelium did not display any morphological or cytochemical manifestations of secretory activity, it is suggested that direct incorporation of exogeneous proteins into yolk may play a lesser role in vitellogenesis in these forms than in insects and many other animal groups. Ooplasmic RNA levels achieved a maximum before vitellogenesis was initiated and then decreased. Similarly the nucleoli increased in size and RNA content up to the point at which cytoplasmic RNA levels began to decline. Basic proteins associated with RNA were present in the oocyte cytoplasm and the nucleoli. These achieved a peak concentration in the same size oocytes as RNA, but the intensity of staining decreased more rapidly than that of RNA during subsequent growth. The concentration of nucleoplasmic protein in oocytes of all four millipede species increased in the germinal vesicles during the course of oocyte growth. Coincident with the initiation of vitellogenesis, a class of cytoplasmic inclusions was developed which have been called “concentric ring bodies”. These inclusions consist of concentric layers of organic matrix material with crystallized calcium salts sandwiched between. These probably represent calcium reserves which are utilized in the formation of the exoskeleton by the embryo.