SUMMARY OF CURRENT RESEARCHES. 13 



cells also give rise to germinative cells. The formation of primordial 

 genital cells is due to the absorption by the cells named above of a large 

 amount of yolk, and the gradual assimilation of this yolk. During the 

 process there is no division of the primordial cells, their increase in 

 number being due to the transformation of the peritoneal and mesen- 

 chymatous cells. When the yolk is completely assimilated, however, 

 the primordial genital cells, which may now be called the primordial 

 ova, are surrounded by small germinative cells, and begin to divide by 

 mitotic division. This division, which is synchronous with changes 

 in the ovary itself, is associated with a remarkable degeneration and 

 expulsion of a certain number of primordial ova into the body-cavity ; 

 a phenomenon more striking in future males than in the females. At 

 the same time certain of the small germinative cells are converted into 

 primordial ova. At the same stage the mesenchymatous Wolffian tissue 

 grows into the developing ovary, and forms the medullary cords in 

 which the cavities of the ovary appear. These cavities are therefore 

 the homologues of the tubules of the testis in the male, and are more 

 numerous in the tadpole than in the adult. The corpora adiposa develope 

 at the expense of a part of the genital organ which contains no primor- 

 dial ova, and are homologous with the interstitial cells of mammals. 

 The primordial 'ova give rise by repeated division to nests of oogonia, 

 each nest lying within the primordial follicle formed by the germinative 

 cells. The nuclei of the oogonia then undergo remarkable changes, 

 suggesting the approach of division ; but this does not occur, the nuclei 

 are reconstituted, and the oocytes are thus differentiated from the 

 oogonia. Thus the oocytes each arise from a single oogonium (con- 

 trast Goette, Nussbaum, &c). All the oogonia do not give rise to 

 oocytes, for a certain number degenerate and disappear, but in each nest 

 of oogonia several oocytes are generally formed. The author has not 

 carried his researches beyond this point. 



Defences of the Ovum.* — Dr. G. Loisel has published an interesting 

 essay on the various ways (by reserves, envelopes, ivc.) in which the 

 ovum may be protected against drought, extreme humidity, heat, cold, 

 microbes, and other injurious influences. The protection enables the 

 ovum to survive in its struggle for existence, which is particularly keen 

 in the period between liberation from the ovary and the beginning of 

 development. All the ova of the same age are not identical ; they vary 

 partly in the adequacy of their protection ; those that succeed are, often 

 at least, the most effectively protected. In short, there is important 

 selective action and also modification in the earliest stages of life. 



Alleged Amoeboid Movements of Germinal Vesicle.f— A. Giardina 

 is entirely sceptical as to the occurrence of active amoeboid movements 

 in the germinal vesicle. The apparent movements are passivo, and 

 are due to differences of concentration in the surrounding substances. 



Abnormal Eggs of Tropidonotus natrix. J — G. Wetzel describes 

 three cases of abnormality in developing eggs of this snake. In one of 



• Journ. Anat. Physiol., xxxvi. (1900) pp. 438-63. 



t Rivista Sci. Biol., ii. (1900) pp. 1-11 (2 figs.). See Zool. Centralbl , vii. (1900> 

 pp. 786-7. 



X Anat. Anzeig., xviii. (1900) pp. 425-40 (5 figs.). 



