540 Theophilus s. Painter. 



a study of the growth period. The first is the appearance of a 

 large number of supernumerary chromosomes free in the nuclear 

 cavity, and the second is the early appearance of the centrosomes. 

 The latter was very puzzling at first. Even as early as the lep- 

 totene period one may find very densely staining granules lying in 

 the cytoplasm of the cell. We find the same in the pachytene stage. 

 During the first maturation division the centrosomes appear to be 

 made up of two elements (Figs. 71, 74, 75). At first it was thought 

 that one of the very small chromosomes had dividied early and 

 gone to the poles of the cell; but after a study of the granules, 

 which appeared so early, I became convinced that the centrosome 

 was really composed of two elements, and these were to be derived 

 from the granules which appeared early in the cytoplasm. 



The granules are large and are very conspicuous as they lie 

 in the cytoplasm of the cell. The maximum number seems to be 

 four, and these may sometimes be all seen in one section (Fig. 70). 

 There is a difference in the size of the granules, one being constantly 

 smaller than its mates, while the three remaining are all about the 

 same size. This same size relation holds for the centrosomes of 

 the spindle, as a glance at Fig. 71 will show. Here one centrosome 

 is made up of two equal-sized particles, while the other is made 

 up of one larger and one smaller element (Fig. N). The position 

 of the granules is variable through the whole growth period. Some- 

 times a pair will be seen on opposite sides of the nucleus, but more 

 usually they are scattered in an irregular manner through the 

 cytoplasm. It is not until the early prophase that the granules 

 take up their positions on opposite sides of the nucleus. 



Prophase. After the second contraction, the autosomes lie 

 free in the nuclear cavity, and, in Fig. 0, drawings of a few typical 

 chromosomes have been given. The most interesting point, which 

 a study of this period brings out, is, that the supernumerary 

 chromosomes show up as individual bodies at this time and lie free 

 in the nuclear cavity or close to some autosome. I have not been 

 able to identify the accessory chromosomes during the early prophase, 

 so it can not be stated what its condition is with regard to the 

 supernumerary bodies. It is possible that the chromosome marked 

 „^" in Fig. 0, is the former body. 



A careful study was made of the relation of the supernumerary 

 chromosomes and the autosomes in order to determine whether there 

 was any definite association between these bodies. My observations 



