468 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [14] 



cells uever precedes the conjugatiou of the egg aud the spermatozoou, as 

 appears to be the case with the eggs of Ostrea virginica and 0. angulata. 

 The account given by OEUacher of the disappearance of the genninative 

 vesicle in the egg of the trout will evidently not hold for that of the cod, 

 where there is no germinal disk developed at the time of the maturation 

 of the egg. Here, as in the shad, the vesicle has already disappeared 

 as such while the egg was still within the follicle, but my eflorts to study 

 the metamorphosis of the germinative vesicle in ova of varying grades 

 of maturity in the lobules of the ovary led me to no definite or valuable 

 conclusions. The ripe eggs lose the whitish color of the less mature 

 ova which still have the germinative vesicle imbedded in their centers. 



(Ellacher has given the following account of the disappearance of the 

 germinative vesicle in the egg of the trout: "The germinal vesicle ap- 

 proaches the periphery of the egg and is enveloped by the germinal 

 matter while still within the follicle. The germinal vesicle of the trout 

 egg recently escaped from the follicle is, according to my observations, 

 wholly eliminated. I have described the whole series of phenomena 

 which occur duriug this elimination in Max Schultze's At-cMv fur mik- 

 rosJcopische Anatomic, Vol. YIII, and figured in different phases of the 

 same. The process is briefly as follows : In the egg recently freed from 

 its follicle the germinal disk is aggregated at a certain time in a de- 

 pression on the surface of the yelk sphere. In it the germinal vesicle is 

 embedded, opening on its surface by a fine pore. The thick wall of the 

 vesicle, which is traversed by fine pore canals, and in close contact with 

 the germinal matter, begins to manifest contractions, is ruptured, and 

 is finally spread out upon the surface of the germ in a circular form. 

 By this means the contents of the germinative vesicle, in the form of a 

 finely granular spherule, are eliminated from the germ. I once observed 

 that the contents of the germinative vesicle were divided into two 

 unequal spheres."* CEllacher then figures the case of a trout egg in 

 which the germinal vesicle has divided, and has been expelled from the 

 germinal disk as two dissimilar globular bodies. These two bodies may 

 well be the two polar cells of other embryological writers. It seems to 

 me highly improbable that an actual elimination and dissolution of a por- 

 tion of the substance of the egg takes place, such as is here described. 

 We will describe further along what may possibly be regarded as polar 

 cells in the cod's egg. The early contractions of the germ disk of the 

 trout are well described by (Ellacher, and seem to be usually met with 

 by investigators who have studied the development of fishes. The polar 

 cells of the shad egg, or what I at one time regarded as such, I now think 

 are probably a result of abnormal development, and not to be considered 

 in this connection. 



Salensky,t in his preliminary account of the development of the ster- 



* Zeitsch. f. lom. Zoologie, XXII, 1872, pp. 40G-J07. 

 t Zoologiecher Anzeiger, I, 1878, pp. 24l?-244. 



