286 



The small round nucleus stains more deeply than the normal nuclei 

 and its structure is so dense that few details can be distinguished. In 

 no case, however, have I observed this condition in more than one 

 nucleus of a pair. 



Believing that counts of the number of nuclei and the number of 

 amitoses in various regions might be of some interest I counted the 

 number of mitoses in that portion of the embryo lying between the 

 lateral borders of the mesoblastic somites in thirteen transverse sec- 





•.«^:-#^ 



VII 



tions of the fifth and sixth somites of the ten-somite stage. These 

 sections included practically the whole of the two somites. The total 

 number was 88 : As I had noted frequent mitoses in the region lateral 

 to the somites and in the membranes. I counted in the same sections 

 the mitoses in a region measuring about V* ^^ adjoining the somites 

 on each side. Here the total number of mitoses was 44, half as many 

 as in the rest of the embryo. Counts and estimates of the number 

 of nuclei in the two regions showed that the middle region including 



