312 



H. H. NEWMAN. 



3. By means of heterogenic hybridization, which always 

 effects a lowering in the rate of development. 



All monsters then seem to be the result of a lowering of develop- 

 mental rate. 



Let us now return to a consideration of hybrid monsters and 

 ask ourselves the question : how does the foreign sperm lower the 

 rate of development? Various views are held as to the way in 

 which the foreign sperm retards development. 



Moenkhaus holds that the foreign sperm exercises a poisonous 



4 



or toxic effect in proportion to the distance of the cross. Loeb 

 holds that the results are due to the inability of the hybrid to 

 digest the yolk with sufficient rapidity. I have expressed the 

 view that there is an incompatibility between the nuclear ele- 

 ments of the two different species that results in abnormal 

 chromosome arrangements and irregular distributions of the 

 latter to various cells. Undoubtedly also the cleavage mechan- 

 ism works less perfectly when chromosomes of very different size 



