1902.] NICHOLS— SPERMATOGENESIS ONISCUS ASELLU3 LINN. 83 



The reconstruction of the nucleus consists of the breaking up of 

 the chromosomes into fine granules, which are connected by linin 

 threads of great delicacy, and in the development of a nuclear 

 membrane (Figs. 19, 20, 21). The change in chemical composi- 

 tion of the chromatin is indicated in sections stained with saffranin 

 and gentian violet by a gradual change in color from red to blue. 

 As the cell body constricts slight thickenings are discoverable on 

 the connective spindle-fibres in the equator (Fig. 18), which, as the 

 constriction proceeds, grow fewer in number and more conspicuous 

 in size until they are finally reduced to a single large swelling, from 

 which radiate the spindle-fibres, by this time grown faint (Fig. 19). 

 At a stage a little later than the one just described I have occa- 

 sionally seen a small black body wedged in the angle between the 

 daughter cells (Fig. 20). Its appearance is similar to the " Flem- 

 mingscher K5rper " described by Hoffmann (1898) for Limax 

 maximus (see his Figs. 31, 32, 33) and strikingly like that of the 

 rabbit described by von Winiwarter (1900, Figs. 9 and 10). 



2. Growth Period. 



The anaphase of the last spermatogonic division is decidedly 

 different from that just described. The chromatin threads lie 

 massed together and entangled near the centre of the cell (synap- 

 sis). They are surrounded by a clear space bridged over by 

 slender acromatic fibres, which connect the chromatin threads 

 with a narrow layer of cytoplasm lying close to the cell wall. No 

 trace of centrosome or sphere substance (idiozome) is discoverable 

 (Fig. 22). The chromosomes now spread apart, although still 

 connected by strands of linin. They are seen to be for the most 

 part V-shaped. The chromatin granules are rather irregularly dis- 

 tributed, being frequently massed together in lumps (Fig. 24). 



In a thin section of a cell at a stage slightly later than this there 

 appeared a minute black dot, surrounded by a vaguely defined 

 area, slightly more dense than the rest of the cytoplasm (Fig. 23). 

 I hesitate to attach importance to this, as it occurred in very few 

 cases. 



The threads now elongate, and during this process the granules 

 of which they are made up divide, so that the thread becomes 

 longitudinally split. The granules apparently do not divide simul- 

 taneously. Even in the same thread some of them show division, 

 while others remain entire (Fig. 25). The split is to be seen with 



