MICHIGAN ACADEMY OF SCIENCE. 73 



NOTES ON THE LATE HISTORY OF THE GERMINAL 

 \'ESICLE IN CRYPTOBRANCHUS ALLEGHENIENSLS. 



BY BEHTRj^M G. SMITH. 



The observations here recorded are sn[)plemeiitary to the account 

 of the history of the ovarian ejig- contained in I'art I of ''The Em- 

 brj'ology of Cryptobranchns"* (Smith, IDllii. 



THE GERMINAL VESICLE' AT THEl SURFACE OF THE EGG. 



The quest ion of flic iidtiirc of ihc op<iqiic globules. At tlie time 

 when tlie egg is ready to leave the ovary, the germinal vesicle is a 

 conspicuous object at the surface of the egg at the animal pole (PI. 

 A' A). In the living egg, the contents of the germinal vesicle con- 

 sist for the most part of clear liquid; but floating at the surface are 

 usually to be found some opa(iue white globules readily visible to 

 the nalced eye. These were successfully photographed, but lost much 

 in distinctness in the lialf-tone reproduction. In the paper above 

 cited T suggested that they might be nucleoli. To be sure, they are 

 much larger and fewer in numl)er than the numerous snuiU nucleoli 

 nsually found at the center of the germinal vesicle of eggs that have 

 l)een stained and sectioned; but it occurred to me that this dif- 

 ference might be due t<» the action of reagents used in fixing and 

 l»reserving. The point seemed worthy of investigation. 



TJw action of reagents on the nucleoli. The study of the effects 

 of some reagents on the nucleoli was undertaken primarily in order 

 to determine whether the opaque objects seen from the surface were 

 the real nucleoli unaffected by reagents. It was conceived that the 

 nncleoli might be broken up and in part dissolved by the acetic acid 

 used in the fixing reagents, or by the acids present as impurities in 

 the formalin used for fixation and preservation. Hence eggs were 

 fixed by two methods not involving- the use of an acid ; Neutralized 

 fonnalin followed by Miiller's solution, and bicliromate-fonnalin 

 in which the formalin was neutraliaed. In both cases the nucleoli 

 appearing in sections seemed precisely the same as if acetic acid 

 or ordinary formalin had been used in the fixing solutions. The 

 results afford evidence that the nucleoli are not identical with the 

 opaque globules seen from the surface, and, what is perhaps of 



♦The Embryology of Cryptohranchus allegheniensis, Pt. I, Jour. Morpliologv. vol. 

 23, No. 1. March. 



