1902.] NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINX. 77 



THE SPERMATOGENESIS OF ONISCUS ASELLUS LINN.» 



WITH ESPECIAL REFERENCE TO THE 



HISTORY OF THE CHROMATIN.' 



BY M. LOUISE NICHOLS. 



(Plates XI-XVIII.) 



{Read April j^, 1902.) 



This study was begun in the month ot February, 1899, i" order 

 to ascertain the mode of origin of the peculiar spermatozoa of the 

 land Isopods. I have now completed, so far as I am able at the 

 present time, the investigation undertaken for that purpose. Before 

 entering, however, upon a description of my observations, I wish, 

 at the close of a work which has proved both interesting and 

 instructive, to express my gratitude to my instructors. Prof. E. G. 

 Conklin and Prof. Thomas H. Montgomery, Jr., for the inspiration 

 and the many valuable suggestions which have aided me toward its 

 completion. To the latter I am particularly indebted for his help- 

 ful criticism concerning the earlier stages of the spermatogenesis. 



Methods. 



The material was fixed either in Flemming's fluid, Hermann's fluid 

 or in Gilson's fluid (acetic-nitric sublimate). It was stained for 

 the most part with iron haematoxylin, but for purposes of compari- 

 son also with saffranin and malachite green (Wilcox) (1895), 

 saffranin and gentian violet, Delafield's haematoxylin and Bordeaux 

 red, and with the Biondi-Ehrlich triple stain. The study of the 

 spermatozoa was also pursued by teasing apart the vas deferens 

 with needles, staining the fresh material with haematoxylin or with 

 acetic-methyl green, and mounting in glycerin. Permanent mounts 

 were also made of fixed and stained material. I consider Wilcox's 

 double stain with saffranin and malachite green to be a valuable 

 one, for the reason that it can be used with good effect on material 

 fixed in Flemming's fluid. It gives in reality a triple stain, for in 

 successful preparations the cytoplasmic structures stain green, 

 active chromatin, centrosomes and true nucleoli red, while resting 

 chromatin takes a purple color. Its chief disadvantage is that it 

 will in time fade. 



iThe species was determined by means of the works of Budde-Lund (1885) 

 •and of Richardson (1900). The species is also known as 0. murarius, Cuv. 



2 A thesis for the degree of Ph.D. at the University of Pennsylvania. 



