470 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [16] 



of wliic-li :ii)i)r();i(;lies the male i)ronncleiis, becoiiK^s more ne;iily louiid, 

 jind iiiiall.v assumes the ovoidal form of a nucleus. In the course of 

 further development the two pronuclei approach each other more closely, 

 and linally blend tog^ether into one nucleus, which represents that of 

 tlie first ck^iva^e, and in its histological characters is perfectly like the 

 l)r()nuclei; it is without a wall, and consists of finely granular, almost 

 liomo<Tfeneous matter." 



Schenk's account of the metamorphosis of the germinal vesicle of the 

 ray is somewhat like that of CEllacher's regarding the trout, except 

 that he does not state that it is eliminated in a similar manner. Alex. 

 Schultz asserts that the appearances seen by Schenk are the result of 

 the action of reagents,* 



4. —Development op the germinal disk. 



As a,lready remarked, the vitellus of the cod's egg is composed of a 

 thin external layer or pellicle of germinal matter, which incloses the 

 yelk substance, which forms by far the largest proportiou of the whole 

 vitelline mass. The outer iiellicle {DoUerUaut of Q^llacher ; couche inter- 

 mediaire, Van Bambeke) may be regarded as theproto2)Iasm from which 

 the germ is formed, while the contained yelk, which is broken down into 

 leucocytes during development and later embryonic growth, is the deu- 

 foplasm. These structures are the homologues of similar parts in other 

 Teleostean eggs as well as in those of the Ghondrostei, or sturgeons, as 

 we perceive by the description of the ova of the latter by Saleusky. 

 The layer ;9r and the contained mass d of Fig. 1, pi. I, corresi)ond to these 

 two elementary portions of the vitellus of the cod's egg. 



The formation of the germinal disk of the cod by a kind of amoeboid 

 migration of the peripheral germinyl matter towards the lower i)ole of 

 the egg is one of the most remarkable phenomena in the history of the 

 development of Teleostean eggs which has hitherto been recorded. The 

 amoeboid movements which accomi)any the development of the disk are 

 most striking, and cannot fail to arrest the attention of the observer, in 

 that as soon as a i)erceptible thickening or accumulation of germinal 

 matter has gathered at the lower pole, the germinal protoplasm mani- 

 fests active changes of form, due to its contractility. These ])ass over 

 tlie inci])ient disk as waves of contraction, and accompany the process 

 of development of the disk long before any sign of segmentation has 



* lu tliis connection I may remark tbat chromic acid, followed by alcohol, or the firat 

 alone, will Hometimes produce changes in the yelks offish ova of a very remarkable 

 fharactor. In illnstration, I recall the alterations so induced in the yolks of the eggs 

 of the shad. Sonustimes the ettect produced by the shrinking and coagulation of the 

 douToi)lasm is to develop a complex system of anastomosing canals imd spaces, which 

 at lirst look like as if they were truly normal features in sections. Fiu'ther investiga- 

 tion has convinced me that these tubular cavities are purely tlie result of the action 

 of chromic acid upon the proteids of the yelk. Doubtless, structures of this kind 

 hav<! misled other investigators, judging fjom observations which arc upou record. 



