BIGELOW: NUCLEAR CYCLE OF GONIOXEMUS MURBACIIII. 317 



living cell that this question can be definitely settled, and I trust that 

 such a study of Gonionemus will not long be delayed. 



Having, then, disposed in this way of the pseudosynapsis phases, I 

 return to the consideration of the normal stages in the later prophase, 

 leading to the formation of the individual chromosomes. To trace 

 these in detail has been difficult, on account of the small size of the 

 cells, yet the following phenomena are fairly well established. The last 

 stage described (Fig. 47) was the " modified spireme," characterized by 

 a thick, smooth, strongly staining chromatin net having comparatively 

 few meshes. I have not been able to find any evidence here, any more 

 than in the entoderm cells (page 298), or in the spermatogonia (page 

 306), that this net is ever metamorphosed into a continuous spireme 

 thread. On the contrary, the next change appears to be the segmenta- 

 tion of the net, or rather of its chromatin component, into a consider- 

 able number of separate chromatin masses, which are roughly spherical, 

 dense, and sharply outlined, but still remain connected to one another by 

 delicate linin strands (Plate 4, Fig. 56). This is a stage in which con- 

 traction very commonly occurs (Figs. 54, 55), so much so that I at first 

 believed that the strands which contract to form the " pseudosynapsis " 

 phase emerged therefrom segmented ; this, too, is the course of events 

 described by Guenther (:04) in Hydra viridis. The number of these 

 masses, the chromomeres, is of course of great theoretic importance, and 

 I have therefore made many counts. Absolute accuracy in these is per- 

 haps impossible, certainly it is very difficult ; but the counts varied 

 always from 23 to 2G or 27, from which I infer that their actual num- 

 ber is probably twenty-four, and thus exactly equal to that of the chro- 

 mosomes in the spermatogonia, and only half as great as that of the 

 chromomeres in the same cells. Moreover, they are decidedly larger 

 than the latter (compare Plate 2, Fig. 23, with Plate 4, Fig. 56). The 

 nuclear membrane now breaks down, and the nuclear space becomes 

 filled with cytoplasm, in which the chromatin structures lie more or less 

 irregularly arranged, being still connected by the persistent achromatic 

 strands, and less crowded than in the case of the spermatogonia. They 

 also become more sharply outlined, denser, and stained more deeply 

 (Figs. 57, 58). Enumerations of all favorable specimens gave, as 

 before, twenty-four as the probable number of chromomeres. The for- 

 mation of the chromosomes of the first maturation division takes place, 

 as I believe, through the fusion of these chromomeres in pairs, just as is 

 probably true of the spermatogonia, only here, since we are dealing with 

 half as many chromomeres, only one half the somatic number of chro- 



