260 T. H. Morgan 
equal or nearly equal-sized chromosomes and one small one (Figs. 
XV, N-R; XVI,S, T). These two types obviously correspond to 
the two somatic types, and here, as there, all the cells of one embryo 
are alike in that they fall into one group or the other. 
an sz 
Fig. XIII Chromosomes of somatic cells of female embryos. 
At the beginning of the division two of the chromosomes show a 
clear line in the middle where the halves will subsequently sepa- 
