403 p. M. BALFOUR. 



maturity is composed with more or less of distiuctness of two forms 

 of cells. One of these is large flask -shaped and rich in proto- 

 plasm, the other is small, consisting of a mere film of protoj)lasm 

 round a nucleus. Considering that the larger cells ap])ear at the 

 time of rapid growth, it is natural to interpret their presence as 

 connected with the nutrition of the ovum. This view is sup- 

 ported by the observations of Eimer and Braun, on the develop- 

 ment of Reptilian ova. In many Eeptilian ova it appears from 

 Eimer's^ observations, that the follicular epithelium becomes 

 several layers thick^ and that a differentiation of the cells, 

 similar to that in Elasinobranchs, takes place. The flask-shaped 

 cells eventually undergo peculiar changes, becoming converted 

 into a kind of beaker- cell, with prolongations through the egg 

 membranes, which take the place of canals leading to the interior 

 of the egg. Braun also expresses himself strongly in favour of the 

 flask-shaped cells functioning in the nutrition of the egg.^ That 

 these cells in the Reptilian ova really correspond with those in Elas- 

 mobrancl/s appears to me clear from Elmer's figures, but I have 

 not myself studied any Reptilian ovum. My reasons for dissent- 

 ing from both Semper's and Schultz's views on the nature of the 

 two forms of follicular cells have already been stated. 



T//e vitellus and the development of the yolk-spherules. — 

 Leydig, Gegenbaur, and Schultz, have recorded important obser- 

 vations on this head. Leydig^ chiefly describes the peculiar 

 characters of the yolk-spherules. 



Gegenbaur'^ finds in the youngest eggs fine granules, which sub- 

 sequently develop into vesicles, in the interior of which the solid 

 oval spheres, so characteristic of Elasmobranchs, are developed. 



Schultz describes in the youngest ova of Torpedo the minute 

 yolk-sperules arranged in a semi-lunar form around the excentric 

 germinal vesicle. In older ova they spread through the whole. 

 He also gives a description of their arrangement in the ripe ovum. 

 Dr. Schultz further finds in the body of the ovum peculiar jiroto- 

 plastic stria3, arranged as a series of pyramids, with the bases 

 directed outwards. In the periphery of the ovum a protoplastic 

 network is also present, which is continuous with the above-men- 

 tioned j)yramidal structures. 



My observations do not very greatly extend those of Ge- 

 genbaur and Schultz with reference to the development of the 



' 'Arcliiv. fur mikr. Aiiat.,' vol. viii. 



" " 15raun Uroffcnital system d. Ampbibien, Arboiten a. d.," ' Zool.-zoot. 

 Institut AViirzbiirf^,' Hit. iv. He says, in reference to tlie flask-sliaped 

 cell, p. 1()0, " llochstens wiirde ich die Fuuktiou dcr grosbcu Tollikel- 

 zellen als einzeUige Driisen uiclir bctoucu." 



' Log. cit. 



* Loc. cit. 



