No. 2.] FORMATION OF THE FISH EMBRYO. 439 



within a difference of ten for the most extreme cases, generally 

 much nearer together. 



In a cross-section of an embryo, developed from one of the 

 first two blastomeres, passing through the eye-vesicles I found 

 124 nuclei in the central nervecord and notochord. In one 

 eye-vesicle there were 70 nuclei ; in the other, 66. 



The results from the two cases are very close, and, although 

 there is some chance of error in the counting, yet there can be 

 no doubt that the number of nuclei is about the same. 



The absolute number of nuclei in the smaller embryos must 

 be, nevertheless, smaller than in the normal on account of the 

 difference in length of the two embryos. 



The results show, I think, that the smaller embryo, instead 

 of elongation by axial concentration to the full normal length, 

 tends to form an embryo whose cross-section is not greatly 

 different from that of the normal. That is to say, elongation 

 takes place to a less degree where there is less material to 

 expend, and most of the material is utilized to form an embryo 

 approaching the normal, as far as possible, for tht part fanned. 



The number of cells in the cross-section cannot be so satis- 

 factorily counted. Their number must correspond to that of 

 the nuclei present ; hence, since the number of nuclei is the 

 same in the two cases, the number of cells must be also the 

 same. Since the embryos from one of the first two blasto- 

 meres are smaller than the normal, it would seem that the size 

 of each cell in the former must be a little less than in the 

 normal. I do not place much confidence in the last deduction, 

 for it leaves out of account the intercellular spaces, and the 

 chance of error from this source is too great to allow any 

 special weight to be attached to the conclusion regarding the 

 size of each cell. Actual measurements do not show any 

 decided difference in the two cases. 



The conclusions given above are not the result of a compari- 

 son of a few sections, but are the abstract of a large number 

 of observations. Since they all agreed, it did not seem worth 

 while to dwell at greater length on the subject. The fact that 

 the protoplasm that accumulates beneath the embryo, and 

 which belong-s to the removed blastomere, and therefore is at 



