CHROMOSOMES IN EMBRYOS. 



49 



distinctly larger than the others. The second pair of macro- 

 chromosomes is somewhat more difficult to make out. 



The three lower figures (Figs. 4, 5 and 6) are from embryos 

 with tw T enty-one chromosomes. Figs. 4 and 6 are from mesoderm 

 cells of two different embryos, at a stage when the limb buds are 

 first appearing. Fig. 5 is from a cell in the cerebral ganglion 



4 o 



Anasa tristis. Initial magnification of 4,800 diameters, reduced one third. 

 Figs, i and 2, hypodermal layer of the antenna, 22 chromosomes. Fig. 3, cerebral 

 ganglion cell, 22 chromosomes. Fig. 4, mesoderm cell, 21 chromosomes. Fig. 5, 

 cerebral ganglion cell, 21 chromosomes. Fig. 6, mesoderm cell, 21 chromosomes. 



of another individual, at a much later stage of development. 

 In each of these figures the w-chromosomes are easily distinguish- 

 able, and it can be seen that there are two paired and one unpaired 

 macrochromosome, particularly well shown in Fig. 4. Although 

 no attempt has been made to pair the chromosomes, in several 

 of the figures shown it would be quite possible to do so. 



In all the cases studied the twenty-one chromosome groups 

 generally show quite clearly three chromosomes larger than the 

 rest, while the twenty-two chromosome groups show four such 

 chromosomes. In most of the figures the ra-chromosomes stand 



