EMBRYOLOGICAL INVESTIGATIONS 267 



a blastula, and then a gastrula, and ultimately 

 becoming a larva, which differed from a normal one 

 merely in being half the usual size. 



Wilson next took the stage with four blasto- 

 meres, and found that each of the four, if isolated, 

 developed into a larva of typical form, but one- 

 fourth the usual size : if two or three of the 

 blastomeres held together a larva resulted which 

 was half or three-quarters the normal size. It 

 appears therefore that at the stage with four 

 blastomeres, either one, two, three, or all four of 

 the blastomeres have the power of developing into 

 an embryo which will be normal in all respects, 

 saving only as regards size. Anxious to deter- 

 mine the limits to which this extraordinary process 

 could be continued, Wilson tried the next stage, 

 that in which eight blastomeres are present, of 

 which four are rather smaller, and four rather 

 larger in size. Each blastomere when isolated 

 commenced to develop, but never became a 

 complete embryo. Flat plates, curved plates, even 

 blastulas one-eighth the normal size were formed, 

 which swam about freely by means of cilia, but 

 which underwent no further development. 



These results are of very great interest. They 

 must I think be regarded as fatal to the doctrine 

 of " Evolution " in its new form, as maintained by 

 His and Weismann ; for if any one of the first four 

 blastomeres is able by itself to develop directly 

 into an embryo, it seems impossible to hold that 

 each blastomere has a predestined part to play in 

 the formation of the embryo. 



