BIGELOW: NUCLEAR CYCLE OF GONIONEMUS MUKBACIIII. 345 



previously stated, the oogonia lie in groups, chiefly basal, though occa- 

 sionally in other locations ; and all the mitotic figures found in a study of 

 some two hundred sections of the female gonad lie in groups of these 

 cells. The oocytes showing the apparent prophases lie in entirely sepa- 

 rate groups of five or ten cells each, usually crowded between the larger 

 oocytes, never (or very rarely) in connection with oogonia ; in these groups 

 not a single mitotic figure has been observed. The question as to the oc- 

 currence of the reconstruction phases is of importance, since this process 

 is invariably a rather lengthy one, and these, though fairly common 

 among the groups of oogonia, have never been seen among groups of the 

 oocytes. The weight of all this evidence is such that, although it is of 

 course not absolute proof, it seems to me to establish beyond reasonable 

 doubt the contention that the apparent prophase of the young oocytes 

 does not lead to any nuclear division whatever. As to the later fate of 

 this phase of nuclear activity, it has been suggested that it may occur in 

 cells, which, as the result of some disturbance, enter upon a prophase, 

 and then degenerate, or at any rate proceed no further in development. 

 There is no actual evidence whatever in favor of this view; and since, 

 when nuclear degeneration does take place, the stages are always very 

 abundant and conspicuous, it may be discarded without further discus- 

 sion. I believe we must conclude that in this species, or at least in the 

 specimens examined, this pseudoprophase of the oocytes is a perfectly 

 normal stage, which leads, not as might be expected to an ensuing nu- 

 clear division, but, through regressive changes, to a resting condition in 

 which the nucleolus and chromatic bodies exhibit a condition very differ- 

 ent from that seen in the resting stage which preceded it. I say " the 

 specimens examined," for we must remember that in Thysanozoon, one 

 of the two similar cases which I have been able to find in the literature 

 of oogenesis, one observer, Selenka ('8l) : describes a very similar con- 

 dition, while in other specimens of the same species, Schockaert (:0l) 

 was unable to find any trace of it. 



We might naturally expect that it would be very difficult to dis- 

 tinguish the stages in regressive metamorphosis from the progressive 

 stages of the apparent prophase. I believe, however, that the cell shown 

 in Figure 129 represents a step in this process. In this specimen the 

 dissociation of the segments into their component chromatin masses has 

 progressed so far that their individual nature is almost entirely lost. At 

 the same time the achromatic net has grown more complex, and the 

 plasmosome has grown much larger. It is, however, sharply outlined, 

 and shows no evidence that any of the chromatin bodies have coalesced 



