[13] EMBRYOGRAPHY OV OSSEOUS FISHES. 4G7 



ing between the vesicles was the only portion which woukl stain, the 

 vesicles remaining perfectly transparent. From this it was concluded 

 that the contents of the vesicles were not protoplasmic or nuclear, but 

 some indifferent fluid. When immersed in alcohol or ether no change 

 was noticed, so that it was highly improbable that the vesicular contents 

 were oily. 



His has observed that the oil globules of the salmon e^g are sur- 

 rounded by an albuminous envelope ; this is probably only a continua- 

 tion of the protoplasm of the germinal layer, as the oil always has a 

 superflcial i)osition in these forms and is not deeply imbedded in the 

 yelk, as in Brosmiiis, Cybiiinij Parephipims, and Elacate. Meischer has 

 also shown that His is wrong in his belief that the rose-colored oil of the 

 salmon egg is composed of lecithin, but is an oil not coagulable at 

 100° G. nor under the influence of concentrated acids, insoluble in alkalis, 

 very soluble in ether and alcohol, and is invariably removed from ova 

 preserved in a strong solution of the latter. If the egg has been pre 

 viously hardened in chromic acid, and sections are prepared, I find that 

 the places formerly occupied by the oil spheres are shown as circular 

 openings around the edge of the section next the yelk envelope. The 

 oil is almost instantly blackened by osmic acid ; in the unchanged state 

 it swims upon the surface of the water when a fresh egg is crushed and 

 the oil allowed to escape. 



3. — Fate of the germinative vesicle. 



The observer sought in vain in these stained preparations of the ripe 

 imimpregnated eggs for the germinative vesicle, and equally fruitless 

 were his endeavors to discover this structure immersed in the yelk be- 

 neath the germinal disk after the latter had been formed. It is believed, 

 therefore, that it has been broken up before the egg has escaped from 

 its follicle in the ovary, and that its remains have rearranged themselves 

 in some way in connection with the germinal matter. No advance of 

 the germinative vesicle towards the periphery of the egg was ever ob- 

 served in the immature egg, or in those nearly mature, so that it is sur- 

 mised that the process of breaking up takes place with comparative 

 rapidity. Kupffer's search for the germinative vesicle of the ovum of 

 the herring was, according to his own account, as fruitless as my own 

 with the cod's egg. Like the ova of birds, those of flshes seem to lose 

 their germinative vesicle before they leave the follicle in which they 

 were developed. It is a most remarkable fact that in some types, mol- 

 lusks, e. g., the germinative vesicle — egg nucleus — should persist in a 

 central position after maturation, and in others, as, for example, in the 

 ova of Elasmobranchs, Teleosts, and Aves, it disapi^ears or is metamor- 

 phosed by the time of maturity and before the egg has left its parent 

 follicle. Again, it is equally remarkable that in some forms the lyolar 

 cells are developed independently of impregnation, while in others the 

 nuclear metamor^jhosis attendant ui)on the development of the polar 



