1896.] Embryology. 79 



When pieces of the wall of the Echinus blastula are broken off they 

 may form little blastula again and these may gastrulate. When these 

 little blastulae invaginate they tend to form more entoderm cells, in pro- 

 portion to the entire number, than is the case in the normal blastula. 



In Sphaerechinus the normal blastula has about 500 cells and tends 

 to invaginate about 50 ; in Echinus about the same fraction of the whole 

 is invaginated, for of about 1000 cells about 100 go in to form the 



When young gastrula? are shaken they may form abnormal Lame 

 owing, apparently, to changes in the mesoderm inducing abnormal 

 skeletal growths and corresponding abnormal arms. 



Pieces shaken out of the wall of a gastrula will not form into a blas- 

 tula nor into a gastrula. 



Likewise the entoderm when shaken out does not develop. Yet a 

 gastrula that has had its entoderm removed by shaking will continue 

 to grow and form a normal skeleton and arms. 



A paper 8 on cross fertilization and the fertilization of non-nucleated 

 pieces of eggs also by Morgan goes over part of the ground of Boveri's 

 remarkable work. 



It is shown that small pieces of eggs of Echinus miliaris may be fer- 

 tilized and develop as far as to the 16 cell stage. As the number of 

 chromosomes in such cleaving masses is, in each nucleus, half the nor- 

 mal number it is inferred that such cleaving masses are the results of 

 the entrance of one spermatozoa into a non-nucleated piece of an egg. 



In attempting to cross fertilize pieces of eggs of Sphaerechinus with 

 sperm of Echinus it was found that the sperm entered the pieces only 

 in few cases ; there is the same difficulty in crossing pieces of eggs as 

 in crossing the whole egg with foreign sperm. The reverse is also the 

 case; sperm of Sphaarechinus will not readily enter pieces of eggs of 

 Echinus. 



It is, therefore not surprising that no larvae were found that could be 

 traced to non-nucleated pieces of eggs fertilized by a sperm of another 

 species, which is.the great desideratum in attempting to repeat Boveri's 



When the whole eggs of Sphaerechinus are fertilized by sperm of 

 Echinus bastards result that are very variable and not all exact middle 

 states between the larva* of these two species. When the converse cross 

 is attempted the larvaa are " for the most part very abnormal in appear- 

 When the eggs of Spluerechinus are crossed with the^perm of Stron- 

 gylocentratus the larva is \ 

 "Idem, pps. 268-280- 





