DEVELOPMENT OF THE GENERATIVE ORGANS. 711 



they are found in the oviduct shows that they have been passed 

 back into the oviduct, instead of having been deposited. It 

 may also be objected that the development of my germ ova 

 within the epithelial cells of the parovarium is not consistent 

 with the view that they are really germ ova. Brandt [330, 

 Fig. 128], however, gives a remarkable figure of the young 

 ovary of the Amphibian Pelobates fuscus, which presents the 

 same appearance as a section of the parovarium of the 

 Blow-fly. He says it is a tolerably thin section of the ovary, 

 and that ' it consists of an oval ring, smooth externally, bounded 

 by a flattened epithelium, which is tuberculated internally by 

 the projecting ova.' In the figure there is no question as to the 

 position of the ova ; they are clearly represented in the interior 

 of the epithelial cells. 



In concluding this section I would again draw attention 

 to the fact that the original structure of the genital cord and 

 the ovary are identical, so that the parovarium is merely a 

 differentiated portion of the ovary, one portion of which be- 

 comes a vitellogenous gland and the other a germ-gland. 



h. On the Changes which occur in the Germinal Vesicle and Free 



Nuclear Formation. 



It was formerly believed that the germinal vesicle disap- 

 pears either before or immediately after fertilisation. Milne 

 Edwards [361], expressing the opinion of the majority of his 

 contemporaries, said : ' The disappearance of the germinal 

 vesical is a consequence of its natural death,' and Leuckart* 

 expressed the same idea in different words ; he regarded the 

 germinal vesicle as ' Concerned in the elaboration of the ovum, 

 but not in the development of the embryo.' 



Johannes Muller [359], in 1852, declared that the germinal 

 vesicle does not disappear in the egg of Entoconcha mirabilis, 

 but that it divides and produces the first pair of segmentation 



* R. Wagner's ' Handworterbuch der Physiologic,' art. ' Zeugung,' by 

 Leuckart. 



