431 F. M. BALFOUR. 



ovaries. Even in the adult Anii)hil)ian ovary, columns of cells 

 of the germinal epithelium, some indiSVrent, others already 

 converted into ova, are present, and, as has been pointed out by 

 Hertwig,' represent Pfliiger's egg-tubes. 



The formation of the permanent ova. — The passage of primitive 

 ova into permanent ova is the part of my investigation to which 

 the greatest attention was paid, and the results arrived at for 

 Mammalia and Elasmobranchii are almost identical. Although 

 there are no investigations as to the changes undergone by the 

 nucleus in other types, still it appears to me safe to conclude 

 that the results arrived at hold good for Vertebrates generally.^ 

 As has already been pointed out the transformation which the so- 

 called primitive ova undergo is sufficient to shew that they are 

 not to be regarded as ova but merely as embri/onic sexual cells. 

 A feature in the transformation, which appears to be fairly 

 constant in Scylhum, and not uncommon in the rabbit, is 

 the fusion of the protoplasm of several ova into a syncytium, 

 the subsequent increase in the number of nuclei in the syn- 

 cytium, the atrophy and absorption of a portion of the nuclei, 

 and the development of the remainder into the germinal vesicles 

 of ova; the vitellus of each ovum being formed by a portion of 

 the protoplasm of the syncytium. 



As to the occurrence of similar phenomena in the Vertebrata 

 generally, it has already been pointed out that Ed. van Beneden 

 has described the polynuclear masses in Mammalia, though he 

 does not appear to me to have given a complete account of their 

 history. Gotte^ describes a fusion of primitive ova in Amphibia, 

 but he believes that the nuclei fuse as well as the bodies of the 

 ova, so that one ovum (according to his view no longer a cell) 

 is formed by the fusion of several primitive ova with their 

 nuclei. I have observed nothing which tends to support Gotte's 

 view about the fusion of the nuclei, and regard it as very im- 

 probable. As regards the interpretation to be placed upon the 

 nests formed of fused primitive ova, Ed. van Beneden maintains 

 that they are to be compared with the upper ends of the egg 

 tubes of Insects, Nematodes, Trematodes, &c. There is no doubt 

 a certain analogy between the two, in that in both cases certain 

 nuclei of a polynuclear mass increase in size, and with the 

 protoplasm around them become segmented off from the re- 

 mainder of the mass as ova, but the analogy cannot be pressed. 

 The primitive ova, or even the general germinal epithelium, rather 



' Loc. cit., 30. 



' Since writing tlie above I Iiavc made out tliat in the Rcptilia t)ie for- 

 mutioii of lh(- perniaiK lit ova takes place iu liic same fashiou as in Elasnio- 

 brancliii and Mammalia. 



' ' Entwicklungsgeschichte, d Uuke.' 



