58 ROBERT SCHARFF. 



ened by an observation which was published by Ransom 1 in 

 1867, in the ' Philosophical Transactions. ' He says : " The 

 action of the water is not the same on the free uninjured ger- 

 minal vesicle in young ova as it is on those still within the 

 egg. I found that the results were in a great measure due to 

 the influence exerted by the constituents of the yolk, which 

 were carried into the vesicle by osmose. When the ovum was 

 acted upon by water, the germinal spots were gradually seen 

 to become pale, and finally disappear. These facts strongly 

 suggest the notion that the germinal spots are soluble in some 

 of the constituents of the yolk, and we may thus explain their 

 disappearance in ripe ova. 



Ransom likewise observed that in the earlier ovum of 

 Gasterosteus leiverus and pungitis — the two species 

 which he examined — the germinal spots, which were embedded 

 in the colloid matrix of the vesicle, were to be seen at the 

 periphery of the vesicle only, so as to be in contact with the 

 inner surface of the nuclear wall. The germinal spots were 

 often " tailed and vacuolate." 



In an older stage, such as that represented by fig. 8, the 

 dark ring encompassing the nucleus has evidently been ab- 

 sorbed, and the latter has dimished in size while the egg itself 

 has continued to grow larger. Indications of the boundary of 

 the old germinal vesicle are still seen (fig. 9, n' .), and the space 

 between it and the reduced one is filled with dark granular 

 protoplasm, which seems still to be produced by the action of 

 the nucleus. A new process, however, begins at this stage, 

 namely, the formation of the yolk spherules, which will be 

 described in the next paragraph. 



II. The Larger Ova and the Formation of the Yolk 



Spherules. 



If we look at figure 9, which represents the nucleus of a 

 large egg surrounded by a zone of protoplasm indicating the 



1 Ransom, "Observations on the Ovum of Osseous Fishes," 'Phil. Trans- 

 actions,' vol, clvii, 1867. 



