30 PROCEEDINGS OF THE AMERICAN ACADEMY 



altogether satisfactory. The embryos are brittle, and the boundary 

 lines between the different parts are not always sufficiently clear. 

 A few of these stages were hardened in Perenyi's fluid,^^ and the 

 sections have proved much more instructive than any obtained from 

 eggs hardened in other fluids. Perenyi's fluid consists of four parts 

 of nitric acid (ten per cent) ; three parts of alcohol (ninety per cent) ; 

 and three parts of chromic acid (one half per cent). 



Perenyi recommends leaving eggs from four to five hours in this 

 fluid, then transferring to seventy per cent alcohol (twenty-four 

 liours), strong alcohol (several days), and finally absolute alcohol 

 (four to five days). Two hours' immersion is certainly sufficient 

 for pelagic fish eggs, and probably even a shorter time would do. 

 Among the methods of staining recommended by Perenyi may be 

 mentioned that of mixing borax-carmine or picro-carmine with the 

 hardening fluid. The addition of the staining fluid produces a pre- 

 cipitate, which should be removed by filtering. The filtered mixture 

 both hardens and stains at the same time, which is certainly an ad- 

 vantage. After an immersion of a few hours in this fluid, the eggs 

 should be transferred first to fifty per cent alcohol (five hours), then 

 to successively higher grades. This method of hardening does not 

 render the eggs brittle. 



General Remarks on the Ovum. 



Although historical summaries and general discussions must be de- 

 ferred until our observations are published in full, it may be well to 

 define at once our view in regard to what constitutes the teleostean 

 ovum, since recent authorities differ very much on this point; and to 

 call attention to a few goneral considerations which bear more or 

 less directly on the much disputed question of the origin of the sub- 

 germinal nuclei. Bibliographical references will be limited to such 

 as serve to make clear the points under consideration. 



In harmony with the view generally received since the publication 

 of Genenbaur's ^® researches on meroblastic vertebrate ova, we regard 

 the teleostean ovum as a simple cell, agreeing in all the more funda- 

 mental features of its constitution, not only with the avian, the rep- 

 tilian, and the selachian ovum, but also with the holoblastic ovum of 

 the mammal, of the amphibian, of the cyclostome. of the ganoid, and 

 of Amphioxus. 



i!* Perenyi. "Eine neue Erliilrtungsfliissigkeit." Zool. Anz., No. 119, p. 459, 

 1882. 

 16 Gegenbaur. MiiUcr's Arch., 1861. 



