92 NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINN. [AprU 4, 



sheath and often entirely torn from it, lying twisted and contorted 

 at some distance from the sheath. According to Hermann, 1883 

 (2), the spermatozoa of the Isopods retain their immobility in the 

 oviduct of the female. The function of the extraordinarily long 

 fibres, if the spermatozoa remain motionless, is to me a matter of 

 great perplexity. It becomes still more puzzling if, as my prepa- 

 rations seem to indicate, there is no direct connection between 

 them and the nuclei. Their function and their true relation to the 

 nuclei might possibly be elucidated by a study of their behavior 

 in fertilization, a study in which I hope to engage at some future 

 time. 



5. T/ie Nucleolus. 



In the resting spermatogonia the nucleolus is present as a rounded 

 or oval body, staining pink with the eosin of the Biondi-Ehrlich 

 stain and red with saffranin. When the mitotic figure is fully 

 formed it is, as a rule, no longer visible, nor is it seen in the pro- 

 phase immediately preceding. The newly constructed daughter 

 nuclei likewise show no trace of it (Figs. 10, 14, 20). Possibly it 

 may consist of metabolic products developed in the resting cell and 

 quickly dissolving during or before mitosis. In the synapsis stage, 

 subsequent to the last division of the spermatogonia, the nucleolus 

 is, however, clearly visible, lying to one side of the tangled mass of 

 chromatin threads. 



In the very earliest synapsis of which I have sections it is not 

 discernible (Fig. 22), but as the threads elongate and separate it 

 becomes evident. It continues to be present throughout the syn- 

 apsis and is finally enclosed within the nucleus of the resting sper- 

 matocyte by the development of the nuclear membrane (Figs. 23, 

 26, 28, 29 and 30). Throughout the prophases of the first sper- 

 matocyte it is still to be seen within the nucleus (Figs. 32, 33 and 

 43^), and after dissolution of the nuclear membrane and formation 

 of the mitotic figure it is cast off to one side of the spindle, where 

 it persists for some time (Figs. 47, 51, 52, 55, 61, 65-67 and 6()F). 

 With saffranin and malachite green the nucleolus is very evident, 

 coloring bright red, while the chromatin of the resting cell is pur- 

 ple. With iron haematoxylin it is not so readily distinguished, but 

 with the Biondi-Ehrlich stain it can be seen as a pink body lying 

 to one side of the spindle. 



