54 



Mr. C. E. Walker. 



[Jan. 9, 



The polymorphic nuclear cells apparently continue to divide amitotically for 

 a number of generations. It is impossible in the present brief communica- 

 tion to illustrate all these stages, but fig. 5 shows two of the most striking. 



At present it is impossible to discriminate between the cells arising amitoti- 

 cally and those arising mitotically from the myeloplaxes. 



Among the mononuclear cells of the bone-marrow and the germinal areas 

 of lymphatic glands, mitotic division figures are very frequent. They are 

 also present, but less numerous, among cells found in the blood and the 

 spleen. 



Many of these mitotic figures are of the ordinary somatic type, and nuclei 

 showing the usual somatic spireme are not uncommon (see figs. 6, 7, and 8). 



More rarely a division figure such as those shown in figs. 12, 13, 14, and 

 15 is met with. In many of these it is extremely difficult to make out even 

 a single individual chromosome. In others, however, several can be made 

 out quite distinctly. This is the case in figs. 12, 13, and 14. In fig. 15 

 the chromatin masses are much less clear, but even this is more distinct than 

 is the case in a considerable proportion of such cells. Though it is not 

 easy, on account of the small size of the cells and the difficulty of 

 obtaining good fixation, to count the chromosomes in even a few among 

 a great many cells, in those where anything approaching an estimation of 

 the number is possible it is evident that the number is much smaller than 

 that found in the somatic division figures occurring in the same animal. 

 That reduction in the number of chromosomes takes place in leucocytes has 

 already been pointed out in a previous communication.* 



It would seem, on comparing these figures with fig. 16, which is the first 

 maiotic (heterotype) division from the testis of a guinea-pig, that these two 

 forms of division are similar to each other, but vastly different from the 

 normal somatic division figures found in the same animal (see fig. 7). 



The probability that these division figures are similar to that occurring 

 in the first maiotic division in reproductive cells does not, however, depend 

 only upon the forms of the chromosomes.f their number, or their arrange- 

 ment upon the spindle. Prophases such as those shown in figs. 9 and 10 

 are not infrequent. In these the so-called spireme is seen to be distinctly 

 split and to differ in other ways from the ordinary somatic spireme (see 



* Farmer, Moore and Walker, " On the Cytology of Malignant Growths," ' Eoy. Soc. 

 Proc.,' B, vol. 77, 1906, p. 336. 



t It may here be pointed out that several of the permanent forms of first maiotic 

 (heterotype) chromosomes described by Moore and Arnold have been observed in the 

 division figures dealt with here. (Moore and Arnold, " On the Existence of Permanent 

 Forms among the Chromosomes of the First Maiotic Division in Certain Animals," 

 ' Eoy. Soc. Proc.,' 1006.) 



