BIGELOW : NUCLEAR CYCLE OF GONIONEMUS MURBACIIII. 323 



is little or no growth during the "resting" stage. Since cells of this 

 generation — which lie near the outer surface of the gonad — are found 

 separately and only in small numbers, it is probable that this stage is of 

 but short duration. 



5. The Second Maturation Division. 



The early prophase of the second maturation division presents the 

 same general features as those with which we are already familiar in 

 corresponding stages in both spermatogonia and primary spermatocytes. 

 The reticulum thickens, becomes denser, and stains more strongly (Fig. 

 73) ; the net-knots increase in size, and at the same time the karyo- 

 plasm becomes less dense and finally disappears, leaving the nucleus in 

 the " empty " condition already described in other cell generations. This 

 result follows in the secondary spermatocytes earlier than in their parent 

 generation, and the " pseudosynapsis " phases which, as already men- 

 tioned (page 315), occur in them in considerable numbers, are frequently 

 seen at a stage previous to the disappearance of the nucleolus. They 

 are also much more irregular, and more clearly present the aspect of ar- 

 tificial modifications of the nucleus than they do in the primary sperma- 

 tocytes. Occasionally, as in the cell represented in Figure 79, they 

 present the most typical " pseudosynapsis " appearance, but more fre- 

 quently the contraction is limited to a portion of the reticulum, 

 leaving the remainder unaltered (Figs. 74, 77) ; it may even include 

 the nucleolus (Fig. 76), a condition never seen in the preceding genera- 

 tion. A series of these structures showing various modifications is rep- 

 resented in Figures 74 to 79. Taken by themselves they are of little or 

 no interest, for they would be classed immediately by any student as 

 artifacts, the results, perhaps, of imperfect fixation. 



On account of the very small size of the cells and of the closely 

 crowded condition of the chromatin in the later stages leading up to the 

 metaphase, it has been impossible to follow the prophase in as great de- 

 tail as in the previous cell generations. Unfortunately it is just those 

 processes which are of greatest theoretic importance, — namely, the ones 

 which result in the formation of the individual chromosomes, — that have 

 proved most baffling. Yet certain features of the process can be es- 

 tablished. These are the first visible changes in the resting nucleus : 

 the reticulum thickens and stains more strongly, and the karyosomes 

 become more prominent (Fig. 73), while the nucleolus separates into 

 several distinct masses (Fig. 75), thus in its disintegration exactly re- 



