A STUDY OF SOMATIC CHROMOSOMES. 337 



closest resemblance to these is shown by the chromosomes of the 

 mesoderm cell (Fig. 4). However, in both of these cases the 

 cytoplasmic areas of the cells are much smaller than those of 

 the cells in which the more elongate chromosomes of Figs. 2 and 

 3 appear. This much elongated appearance of the chromosomes 

 is characteristic of both neuroblasts and late cleavage cells, 

 the nuclei and cytoplasmic areas of which are larger than those 

 of the other cells. One must also take into account the fact 

 that the apparent size and volume of the chromosomes is in- 

 fluenced to some extent by the length of extraction of the stain. 

 Realizing this, the figures produced in this paper have been 

 taken from preparations as far as possible stained alike. 



Figs. 5-8 are from embryos showing the 22-chromosome type. 

 Here again the formula of the 22-chromosome complex, pre- 

 viously outlined, is confirmed. There are four macrochromo- 

 somes in each figure, the difference, as contrasted with the 21- 

 chromosome type, being that the largest chromosome is found 

 paired. Fig. 5 is from a late cleavage cell and, as was the case 

 in corresponding plates of the 2 1 -chromosome type, 'the chromo- 

 somes are much elongate. Fig. 6, from a neuroblast in the 

 cerebral ganglion, was drawn from the finest preparation obtained 

 in all the series. The chromosomes are not as large as in Fig. 3, 

 but this figure is taken from an embryo of about stage III, while, 

 as was pointed out, Fig. 3 is from an earlier stage. 



Figs. 7 and 8 are also from embryos corresponding in their 

 development to stage III. Fig. 8 is from a cell in the hypodermis 

 of the antenna. This cell is of small size, and the chromosomes 

 are the smallest of any group shown. 



Fig. 9 is from an oogonial mitosis. The 22-chromosome type 

 found in the developing embryos corresponds to this in the same 

 manner as the 21 -chromosome type corresponds to the spermato- 

 gonial plate. Fig. 10 is from a dividing cell in the oviduct, and 

 furnishes additional proof that the 22-chromosome type is the 

 female type, and is the number characteristic of the somatic 

 tissues as well as the sex glands of the female. 



In addition, cases of double chromosome groups were found in 

 connective tissue cells surrounding the young ovary. These 

 groups correspond to Wilson's report of 44 chromosomes in 

 certain investing cells of the ovary. Since the number is double 



