376 EMBRYOLOGY. 



brandies. Together with the connective tissue separating them, they 

 form the foundation for the cortex of the ovary. Afterwards they 

 are covered over on the side toward the body-cavity with a thick 

 continuous layer of connective tissue, which becomes the albuginea 

 of the ovary ; they are thereby more sharply separated from the 

 germinal epithelium, (fig. 216 k.e), which is still preserved, even after 

 this, as a layer of cubical cells upon the albuginea. 



There are two kinds of cells to be found in the Pfliigerian egg-tubes : 

 follicular cells and primitive ova (fig. 215y. ande*). Concerning the 

 source of the former opinions are still contradictory (compare p. 382) ; 

 according to my view both arise from the germinal epithelium. 



Whereas the follicular cells become by means of an uninterrupted 

 process of division more numerous and smaller, the primitive ova 

 increase in size continually, and their nuclei become very large and 

 vesicular and acquire a distinctly developed filar network (&&). They 

 rarely lie singly in the cords and balls of follicular cells, but ordi- 

 narily in groups, which are designated as egg-nests. One frequently 

 observes in the nests, as has been announced by BALFOUR and VAN 

 BENEDEN, that several primitive ova become fused into a common, 

 multinuclear mass of protoplasm a syncytium. From this there 

 is afterwards developed usually only a single egg. One of the 

 numerous nuclei soon outstrips the others in size and becomes the 

 germinative vesicle, whereas the remaining ones undergo degeneration 

 and are dissolved. It is not to be concluded from these processes 

 that the egg, as is occasionally asserted, corresponds to a multiple 

 of cells ; the condition is more properly to be interpreted as follows : 

 of the eggs contained in a nest, one outstrips the others in its growth 

 and thereby represses them and employs them, in a certain sense as 

 nutritive material, for its own growth. 



This is a process that occurs very frequently in Invertebrates, and in the 

 phylum of the Arthropods has been studied with the greatest detail by 

 WEISMANN. In these cases the lower Crustacea and Insects one can see how, 

 step by step, out of numerous primitive ova which are originally contained in a 

 germinal chamber of an ovariole, only one becomes the egg, whereas the. others 

 from an early period lag behind in development, then undergo degeneration, 

 and in the form of products of degeneration are taken up as yolk-material into 

 the persisting egg-cell. 



During the enlargement of the egg-cell the second stage of the 

 process of intergrowth of epithelium and connective tissue is intro- 

 duced : the stage of the formation of the follicle (fig. 216). At the 

 boundary between the medullary and cortical zones of the ovary the 



