346 



Prof. Farmer, Messrs. Moore and Walker. [Nov. 17. 



30 



25 



I 



ID Ij 20 25 



Number or chromosomes 



Testis of Periplaneta Americana. 

 F. Curve obtaiued by countings made from dividing nuclei of the maiotic and premaiotic 

 cells of the testis, in order to estimate the probable error in the far more difficult 

 cases of cancer. It will be seen that there is some not inconsiderable variation 

 about the two maxima of 16 and 32. This is due partly to underestimating the 

 number of chromosomes actually present, and partly to the nuclei having in some 

 cases been partly damaged in preparing the section. 



We shall further consider this matter in the concluding part of the paper : 

 at present we are mainly concerned with showing that there exists a 

 striking resemblance between what we have termed the " gametoid " cells of 

 cancer and the cells of normal reproductive tissues, and as we pass to the 

 later phases of mitosis we find the same loop and barrel-shaped chromosomes 

 present in both, and we have occasionally seen, during the diaster of a cancer 

 nucleus, the late longitudinal fission in the daughter chromosomes as they 

 diverge from each other, just as it occurs in the heterotype diaster of so 

 many animals and plants. An inspection of the curves shows the relative 

 frequency of the different numbers of chromosomes met with in the 

 younger cancerous areas. Whilst, as already pointed out, the two maxima of 

 16 and 32 are unmistakeable, it is also obvious that amongst the generally 

 irregular numbers two other groups occur with greater frequency than others. 

 Thus, there is a distinct indication that nuclei containing about 24 chromo- 

 somes may be regarded as forming a distinct group, also that a second, though 

 far less well-marked, series is characterised by containing about 64 (double 

 the normal somatic number) chromosomes. It may be that the latter are 

 related to the ingressiozi of the leucocyte already described, but it is difficult 

 at present to guess at the significance of the grouping of 24. There is no 

 obvious indication that the nuclei with 48 chromosomes are specially common, 

 and, in the absence of more direct evidence, it is useless to indulge in 

 speculations that may prove to be devoid of all foundations. 



