374 T. H. MORGAN AND UM^ TSTJDA. 



Hertwig's conclusions were based on the evidence furnished 

 by certain abnormalities, while Schultze's conclusion rests on 

 a study of normal development. 



It seemed to me at first, from a study of eggs developing 

 normally, that it was impossible that the embryo should lie 

 entirely over the white hemisphere. Schultze pointed out that 

 Roux's earlier results are contradictory in themselves, and I 

 had reached the same conclusion from a careful reading and 

 re-reading of Roux's earlier papers. I was prepared, there- 

 fore, to find some truth in each view, and expected to find the 

 embryo forming partly over the black, partly over the white 

 hemisphere. I was then not a little surprised to find that our 

 studies led to the conclusion that the embryo is formed over 

 part of the white hemisphere of the egg. In the main point, 

 therefore, I am in agreement with Pfliiger and Roux, although 

 not entirely so, for I hope to be able to show the extent 

 of the white hemisphere of the unsegmeuted egg, covered by 

 the blastopore, to be somewhat different from that affirmed by 

 Pfliiger and Roux. 



Our work in relation to the orientation of the embryo has 

 covered the ground somewhat more extensively than that of 

 any previous author, since we have made use of the methods 

 employed by all of them. 



Our results will be considered under three headings : 

 1st. Normal development and location of blastopore. 

 2nd. Results obtained by injury to definite portions of 



the early embryo. 

 3rd. Results obtained from embryos whose development 

 had been modified by artificial means. 

 A word of personal explanation ought to be added. The 

 senior author is responsible for Sections i, iii, iv, and v of the 

 present paper. The work recorded in these was done in the 

 spring of 1893. 



Section ii is the record of the results obtained by Ume 

 Tsuda while a student in the Biological Laboratory of Bryn 

 Mawr College. This work was done during the winter of 

 1891-3; the account written in the spring of 1892. Only 



