[23] EMBRYOGRAPHY OF OSSEOUS FISHES. 477 



after the entrance of the single spermatozoon which effects th<s fertiliza- 

 tion of the egg. Beside these there is a polar process, zapfen, which 

 originates from the middle of the germinal disk as a hyaline proto- 

 plasmic band {axenstrang, Calberla), drawn out by adhesion to the inner 

 surface of the zona radiata from the center of the germinal disk when 

 the zona is lifted up from the latter by the imbibition of the water drawn 

 in through the micropyleor pore canals. Through this process a single 

 effective spermatozoon makes it way into the vitellus, when the hyaline 

 process is withdrawn ; a number of spermatozoa may enter the egg 

 through the micropyle and be enveloped by the hyaline process, but 

 they take no share in the impregnation. Calberla, on the other hand, 

 asserts that but one spermatozoon enters the micropyle and that the 

 tail is left behind, closing up the opening of the latter. In this Calberla 

 agrees with Fol's description of the entrance of the spermatozoon into 

 the egg of the starfish. Scott says he has seen the second polar cell 

 described by Kupffer and Benecke at the germinal pole of the egg. Cal- 

 berla confirms almost fully the previous observations of A. Miiller on 

 the mode of impregnation of the eggs of the lamprey, but his views 

 in regard to the fate of the germinative vesicle are not accepted by 

 Scott. 



The prominence which we noted on the germinal disk of the cod's 

 egg is probably the representative of the extruded polar cells which 

 have been derived from the germinative vesicle. It is not hyaline, as 

 the polar process of the egg of the lamprey has been described to be, 

 but is composed of granular protoplasm. The separate first i^olar cell 

 adherent to the zona radiata of Fetromyzon, upon its inner surface, is 

 something very different from the polar prominence observed in the 

 cod's egg, which reminds one in its main features of the polar cells of 

 moUuscan eggs. It is not so regular in form, however, as these, since 

 it is scarcely ever, if approximately, the same shape in different eggs, 

 often having a jagged appearance or with minute points projecting 

 from the two principal portions. But since the writer did not succeed 

 in witnessing the actual entrance of the spermatozoon into the egg on 

 the breaking up of the germinal vesicle, the final interpretation of the 

 nature of the prominence remains to be elaborated. 



Prof. C. K. Hoffman, of Leyden, in the Zoologischer Anzeiger for 1880, 

 pp. 607-610 and 629-634, gives the following as the result of his inves- 

 tigations, at the zoological station at Naples, of the early stages of de- 

 velopment of JScorpwna, Julis, Grenilahrus, Heliasis, Fierasfer, Syn- 

 gnathus, Hippocampus, Gobius, etc., but more especial attention was 

 paid to the first two on account of the great transparency of the eggs 

 of those genera. 



'' As to ovogenesis my observations fully agree with those of Wal- 

 dcyer, Brock, and Kolessnikow ; the primordial ova originate from tu- 

 bular invaginations of the germinal epithelium of the ovary. The 

 ovarian egg during its whole development is covered by a granulosa, 



