12 CAPT. C. F. U. MEEK ON THE 



The prophase of division is characterized bj the closer association of 

 chromatin granules on the linin threads o£ the reticulum ; and this process 

 continues until the latter is resolved into a number ol; ragged filaments, 

 which shorten and thicken, and later assume a boomerang shape. By this 

 time all trace of the component granules is lost ; and the ragged horseshoe 

 bodies^ folding themselves into figures o£ eight and rings, are gradually- 

 transformed into the smooth and clearly defined chromosomes. The 

 resolution of the reticulum into filaments is shown on Plate 1. fig. 8, and the 

 subsequent shortening and thickening of the boomerangs in fig. 9 of the 

 same Plate. The various shapes assumed by the chromatin filaments at a 

 still later stage are shown on Plate 2. figs. 10-19^ the most prominent types 

 being crosses, rings, and loops. The last-named may be doubled to form a 

 complete figure of eight, or may form a single loop with free ends twisted or 

 crossed over one another. 



As soon as the centrosomes have taken up their position at the poles, the 

 chromosomes appear on the equatorial plate, and the characteristic metaphase 

 figure is once more represented. The heterotropic chromosome remains as a 

 dark and smoothly outlined body close to the nuclear wall while the 

 chromatin filaments are being transformed into chromosomes : it then takes 

 its place among them on the mitotic spindle. The number of filaments 

 evolved from the reticulum is eight, so that nine chromatin bodies compose 

 the metaphase complex. In this manner the sixteen ordinary chromosomes 

 of the spermatogonial cell have been halved, and this reduction must be 

 effected before the breaking up of the spireme, for I have found no evidence 

 of lateral association of filaments after this has occurred. Gerard has 

 obtained similar results, but explains the reduction of the somatic number by 

 describing an association of granules, the reticulum meshes combining in 

 pairs by means of fine anastomosing threads ; he has found that this process 

 always begins near the heterotropic chromosome. On the other hand, Davis 

 denies that a continuous spireme is formed, but mentions a similar massing 

 of granules at this stage ; he describes how the spiremes appear later in the 

 form of loops, attached by their free ends to the nuclear membrane, and, 

 since the number of loops is half the somatic number of the chromosomes, 

 suggests that each loop is composed of two univalent chromosomes united 

 end to end. 



The chromosomes on the equatorial plate exhibit the same size and shape 

 relationships found in the spermatogonial complex : of the eight ordinary 

 chromosomes, three are large, three small, and two of medium size, the 

 heterotropic chromosome again being the fourth largest. This can be seen 

 from Plate 2, where a polar view of the metaphase is given in fig. 20. The 

 smaller chromosomes are the first to divide, division in all cases being- 

 longitudinal ; this agrees with the results of Baumgartner, Gerard, 

 Henderson, McClung, Montgomery, Nowlin, Robertson, Sutton, Wilcox, 



