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



the greatest clearness in sections stained with iron haematoxylin 

 and strongly decolorized. The chromosomes are very irregularly 

 distributed, only occasionally a part of them, six or seven, may be 

 grouped with reference to a central point. Of the entire number 

 of chromosomes present it is difficult to be certain, owing to 

 the fact that they overlie each other so closely. The number, 

 however, is certainly, less than that present in the spermatogonia 

 and not greater than sixteen (Fig. 26). The reduction in the 

 number of chromosomes, therefore, apparently takes place at this 

 stage, and the V-shape so prevalent is due to the approximation of 

 two chromosomes to form a single bivalent one. The place of 

 union is frequently covered by chromatin, but a connection of 

 linin can sometimes be discovered (Fig. 27). This figure also 

 shows the varying angle at which the univalent chromosomes may 

 approach each other. Occasionally they may even form a complete 

 ring. 



The threads become more and more attenuated (Fig. 28), and 

 finally by anastomosis are transferred into the nuclear reticulum of 

 the resting spermatocyte (Fig. 30). During the elongation of the 

 chromosomes the chromatin granules divide and redivide (Figs. 

 33-28), so that they become very numerous, and as the elongation 

 progresses the longitudinal split becomes less easily discoverable, 

 until in the resting cell it can no longer be made out. Cells are 

 sometimes seen in which, just before the formation of the nuclear 

 membrane, the network lies to one side, being connected by slight 

 strands of linin with the surrounding cytoplasm (Fig. 31). 



The fact that the chromosomes remain distinct until just before 

 the formation of the nuclear membrane points to a maintenance of 

 their individuality in the resting cell. 



The nuclear membrane appears to form as a condensation of 

 achromatic substance, upon which later appear granules staining 

 deep blue with haematoxylin (Fig. 29). 



A peculiar fact with reference to the last spermatogonic division 

 has struck my attention and I have been unable to explain it very 

 satisfactorily. It will be seen from Fig. 2 that nearly all the cells 

 in the apical portion of follicle (^b) are in the synapsis stage. It 

 might be supposed from this that sections would be obtained of 

 follicles filled apically with the spindles of the last spermatogonic 

 division. Such a condition, however, I have never found, although 

 I have examined a large number of testes at different seasons of the 



