BIGELOW : NUCLEAR CYCLE OF GONIONEMUS MURBACIIII. 357 



For some reason polar views of this stage were exceedingly rare in the 

 slides at my disposal, and owing to the elongate form of the chromo- 

 somes, it was impossible to count them with any accuracy in side views 

 of the metaphase. But from the conditions obtaining in the late pro- 

 phase, as just described, it is safe to conclude that they are present in 

 the ordinary somatic number, probably twenty-four. Further evidence 

 of this is seen during the anaphase. End views of this stage are com- 

 paratively common (Fig. 151), and it is possible on them to count 'the 

 chromatic structures, though not with absolute accuracy. In all the 

 cases examined the number was about twenty-four, though often appar- 

 ently greater. The apparent excess is probably due to the elongated and 

 constricted form of the chromosomes. I believe, therefore, it can safely 

 be affirmed that the number of chromosomes appearing in the first 

 cleavage spindle is the same as that characteristic of the somatic mitoses 

 of adult tissues. This result is of course just what might naturally be 

 expected, but it assumes special interest in view of the condition of 

 affairs in the second cleavage spindle, to be described shortly. The later 

 anaphase and the telophase present no featimes of peculiar interest. The 

 nucleus passes into the resting condition, in which, however, no nucleo- 

 lus is formed, and the achromatic figure entirely disappears. This figure 

 (Fig. 153) differs very markedly from that seen in the somatic and in 

 the male sexual cells, as will be at once perceived from comparison with 

 the figures on Plates 1 and 2, not only in the possession of prominent 

 asters, but also in the condition of centrosome and spindle fibres as well, 

 for in the present case the interzonal filaments, such a prominent feature 

 of all mitoses in adult tissue, are even now hardly to be distinguished, 

 and later, during the anaphase, break down and disappear. Moreover, 

 the centrosome cannot be detected certainly. The asters themselves, 

 however, persist until the commencement of the re-formation of the 

 nuclei, after which they are no longer to be seen. 



2. Hie Second Cleavage. 



This division (Plate 8, Figs. 155-158) was studied chiefly on whole 

 e<ws fixed in the corrosive-acetic mixture and stained in Grenadier's 

 borax carmine, and on several series of sections ; but no formalin mate- 

 rial was available. The most cursory examination of the second cleavage 

 spindle reveals a general aspect very different from that of the first 

 cleavage, in the condition of both the chromatin structures and the 

 achromatic figure. The second cleavage nucleus during its brief resting 



