190 WM. REES B. ROBERTSON 



it is difficult to distinguish them. In size the sex chromosome 

 falls between 1 and 2, often so nearly like 1 that it is a question 

 which to call it, Ix or 2x. This, again, is a character of the genus 

 Acridium. The sex chromosome passes undivided to one pole 

 of the nucleus in the first maturation division. It always lies 

 outside the plate (figs. 35, 36). 



At the second division (figs. 37, 38) the inequahty in the size 

 of the two largest chromosomes is especially marked and the 

 size relations of all are clearly shown. 



b. Chromosomes of the male somatic cells. The same size re- 

 lations appear in somatic cells though it is more difficult to pick 

 out the members of the smallest and intermediate pairs. In ani- 

 mals taken before the last moult, dividing cells in large numbers 

 were found in the following organs: mesenteron, proctodaeum, 

 hypodermis, fat body, follicles of testis and ovary, and possibly 

 in intestinal muscles. Of these tissues the columnar epithelium 

 of the mesenteron showed the clearest cases of mitosis (figs. 

 39, 40). The cells were too long to be shown complete; accord- 

 ingly only that portion which contains the dividing chromosomes 

 was drawn. In figure 40 the two large pairs and their character- 

 istic inequahty are especially evident. One of the 4's and one 

 of the 3's are seen foreshortened. These cells are of entodermal 

 origin and their chromosomes resemble very much those of sper- 

 matogonia and oogonia. 



Figures 41 and 43 show cells from the posterior part of the 

 alimentary canal, probably of ectodermal origin. The size 

 relations of the chromosomes are the same as before. 



Figures 44, 45, and 47 represent cells from the hypodermis, 

 the layer which secretes the cuticula. These cells contain pig- 

 ment granules, which probably bear an important relation to 

 the pigmentation of the cuticula. The number of chromo- 

 somes and the size relations are the same as in other tissues. 

 The chromosomes are much shortened and thickened and have 

 a tendency to clump together more than usual. 



Figures 48a, 48b, 50a, and 50b are possibly nuclei of fibers 

 from the outer muscular wall of the intestine. The number of 

 chromosomes and the size relations are the same as usual. Fig- 



