438 MORGAN. [Vol. X. 



a side view of a normal embryo ; Fig. B is from an ^g^ operated 

 upon and the largest embryo of which I have a record ; while 

 Fig. C is the smallest embryo of the lot. Generally we find 

 that the embryo from the Qgg operated upon lacks about one- 

 fourth the normal length. 



The breadth of these embryos is always a little less than the 

 normal. This is most obvious in the head after the formation 

 of the optic vesicles. There is here, also, much variation, as 

 shown in the three heads drawn in Figs, ^^i, A, B, C. The 

 first of these is the normal {A), and the other two come 

 from eggs operated upon. The figures are from preserved 

 material. 



The depth (dorso-ventral) of these embryos is generally less 

 than that of the normal, but here, again, there is a great deal 

 of variation. 



These embryos were cut into cross-sections. The cross-sec- 

 tions of the shorter embryos are, in nearly all cases, smaller 

 than the cross-sections of the normal, but the extent of this 

 will depend much on the individual. 



Careful camera drawings of the nuclei of the different organs 

 of the body have been taken and comparisons made between 

 the nuclei of the normal eggs and eggs operated upon. The 

 result is most unexpected. There is no difference in the size of 

 the nuclei of the two sorts of embryos. This holds throughout 

 for nervous system, eye-vesicles, mesoderm and entoderm. 

 When we recall that these nuclei have come from only one- 

 half of the original segmentation nucleus, it is remarkable that 

 at this late stage of development there should be no difference 

 in size of nuclei between the normal and operated embryos. 



Another equally unexpected result was found. If the nuclei 

 in the cross-sections passing through corresponding regions be 

 counted, we find the number practically the same in both 

 normal and operated embryos. As an example of this I may 

 cite one case. In a cross-section of a normal embryo passing 

 through the eye-vesicles I found 117 nuclei in the central nerve- 

 chord and notochord. In one eye-vesicle in section there were 

 67 nuclei, and in the other 65. These numbers are not per- 

 fectly accurate, but are the average of several counts, ranged 



