The Spermatogenesis in Pentatoma up to the Formation of the Spermatid, 45 



the segregation of the chromatin at the two poles of the chromosome 

 is not produced by the agency of mantle fibres. 



Throughout the spirem stages the chromosomes lie close to the 

 nuclear membrane, though this disposition is not clearly shown in all 

 the figures on account of the curved surface of the nucleus. The 7 

 chromosomes, from the end of the loose spirem on, continue to shorten 

 and thicken until the regular dumbbell shape is reached (Figs. 136 

 — 159) ; at the same time they appear to undergo a slight diminution 

 in bulk, probably due to greater concentration of their substance. The 

 constriction of each is still transverse to its long axis, and we shall find 

 that this plane of constriction later comes to lie in the plane of the 

 equatorial plate (Figs. 160 — 169, 172 — 175). The chromosomes attain 

 their definitive form shortly before the nuclear membrane disappears ; 

 their outlines now appear quite smooth, and their substance homogene- 

 ous (Figs. 148 — 159). It is the rule that the chromosomes of a given 

 nucleus vary greatly in volume, the largest having sometimes 6 times 

 or more the volume of the smallest; it is seldom that one finds a 

 nucleus in which all the chromosomes have approximately the same 

 volume. Dififerences in form still persist, but they are not nearly so 

 marked as in previous stages. It is a difficult fact to determine, but 

 it seems that, despite the differences in the volume of individual 

 chromosomes, the sum total of chromatin is approximately the same 

 in all nuclei. This is the case for cells of the large as well as of 

 the small generation; and the fact is important, showing that the 

 amount of hereditable substance allotted to the spermatozoa is ap- 

 proximately the same in all cases, though the morphologically less 

 important substances, such as the cytoplasm and nuclear sap, vary 

 dimensionally very markedly in different cells. Thus notwithstanding 

 the various degrees of nourishment to which individual cells are ex- 

 posed, there would seem to be a regulative process in each cell keeping 

 the amount of chromatin at a given norm. In the growth period of 

 the spermatocytes the chromatin more than doubles its amount 

 (compare the spermatogonic with the spermatocytic monasters); but 

 still the chromatin would appear to grow at the same rate in all 

 cells, even in those of the large and small generations. What is the 

 nature of this regulative factor? The answer is deeply needed from 

 the standpoint of heredity, though it will be probably never settled 

 empirically. As to the mode of growth of the chromatin, I would 

 propose two suggestions. Either we may assume that the chromatin 

 microsomes do not divide in the growth period, but only increase in 



