310 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the plane of division, but more frequently they revolve so as to lie par- 

 allel to the spindle rays, and it is now seen that they once more exhibit 

 the dumb-bell form temporarily lost during the metaphase. In cells 

 partly crushed the condition of the chromosomes appears most distinctly 

 (Fig. 32). Occasionally, when the migration is more nearly simulta- 

 neous, typical daughter plates are formed, and in polar views of several 

 such I have been able to count the chromosomes with comparative accu- 

 racy. Thus, in the cell shown in Figure 34 a and 34 b (Plate 3), viewed 

 somewhat obliquely, I was able to count in one daughter plate 24 

 chromosomes, and in the other apparently 25. This, of course, is addi- 

 tional evidence that in the spermatogonia the chromosomes are present 

 in exactly the same number as in the somatic cells. As they continue 

 to approach the poles, interzonal filaments are formed which appear, espe- 

 cially in vom Eath preparations, much stouter than the spindle fibres, a 

 condition characteristic of all mitoses in adult tissues of Gonionemus 

 (Fig. 35). "With the further migration of the chromosomes, the polar 

 portions of the spindle fibres gradually dwindle, and finally seem to dis- 

 integrate (Figs. 35, 36), though leaving the conical mass of archoplasmic 

 substance focusing at the centrosome still sharply marked off from the 

 surrounding cytoplasm. The interzonal filaments, on the other hand, 

 increase in stoutness with the progress of cell division. This is, of 

 course, exactly the opposite of what we should expect if we were to 

 explain the process of mitosis on the theory of fibrillar contraction. 



Constriction of the cell body now takes place (Figs. 35-38); but the 

 two daughter cells long remain connected by the bridge of interzonal 

 filaments, which bear at their central point a series of distinct Zwischen- 

 korper. Eventually, however, this bridge dwindles and breaks down 

 (Figs. 39, 40), and the remnants of the fibres disappear. The centro- 

 some cannot be traced after the late anaphase ; and its fate is doubtful, 

 for with the disappearance of the spindle remnants there is no longer any 

 index to its position, and it easily becomes indistinguishable among the 

 cytoplasmic microsomes. 



During the anaphase the chromosomes often become very closely 

 crowded (Fig. 36), even appearing to fuse, an event described by Down- 

 ing ( : 05) as occurring in Hydra. In Gonionemus, however, this is not 

 the case, for by careful focusing it is always possible to resolve the mass 

 into separate chromosomes, which now, however, have lost their sharp 

 outlines and are of a more or less granular consistency (Fig. 38). 



The re-formation of the nucleas appears to be essentially like the 

 process described by Lerat (=05) in the case of Cyclops. The chromo- 



