BIGELOW: NUCLEAR CYCLE OF GONIONEMUS MURBACIIII. 311 



somes move somewhat apart once more, and it is seen that they have 

 become connected to form an irregular network (Fig. 38). There is in 

 Gonionemus no evidence that the achromatic strands persist throughout 

 mitosis, as described by many investigators. I believe the true expla- 

 nation is that the chromosomes, while closely in contact, become more 

 or less confluent. It must be borne in mind, however, that every chro- 

 mosome is, no doubt, of mixed origin, chromatic and achromatic, and 

 that the connecting links of the reticulum may thus be formed chiefly, if 

 not entirely, from the achromatic portion of the chromosomes. The net 

 thus formed encloses between its meshes a large amount of cytoplasm. 

 The nuclear membrane now reforms, and the enclosed cytoplasm prob- 

 ably becomes the karyoplasm of the spermatocyte nucleus. 



The threads of the reticulum become more and more homogeneous, 

 until finally the individual chromosomes are no longer distinguishable 

 (Fig. 37). The nucleus, till now much flattened and lying near the 

 periphery of the cell, becomes oval in outline and takes up a more nearly 

 central position. It increases in size, and at the same time the network 

 becomes looser, and fiually disintegrates, its place being taken by deli- 

 cate linin strands, while the chromatin breaks down into numerous 

 microsomes. The reformation of the nucleolus takes place through the 

 aggi-egation of certain of the chromatic microsomes (Fig. 39), just as 

 has already been described in the case of the mitosis of the entoderm 

 cells (page 301). But in the present case stages in the process are so 

 much more numerous that the actual course of events can be established 

 more certainly. The cells now enter upon a period of apparent qui- 

 escence, preparatory to the prophases of the first maturation division. 

 Cells of this stage are usually designated according to the terminology 

 introduced by Boveri in 1891, as the last generation of spermatogonia. 

 I prefer, however, to term them already the primary spermatocytes, for 

 it seems to me more logical to adopt names based on the cell generations 

 rather than on conditions of growth. 



2. Tlie Primary Spermatocytes. 



The spermatocytes of the first generation are, during the resting stage, 

 much smaller than their parent spermatogonia, the diameter of the entire 

 cell measuring only about 8.5 jw and that of the nucleus 6.5 p. Spacial 

 relations within the gonad are of some assistance in determining the 

 cell generations, since the spermatogonia, except in a few isolated cases, 

 lie basally, in contact with the mesogloea, whereas the primary sperma- 

 tocytes in various stages form a broad zone just peripheral to them, and 



