Extraovate Experiments on the Egg 

 of Sea-urchin. 



By 



Naokide Yatsu. 



Zool. Inst., Tokyo Imp. Univ. 



In treating the eggs of Arbacia ten minutes after fertilization with 

 diluted sea-water and in replacing them into ordinary sea-water, LOEB 

 had the good fortune to obtain double or triple larva; developed 

 from the eggs with extraovates ('94a, '94b and '95). The same 

 experiments were repeated by RAWITZ at Rovigno on the egg of Stron- 

 gylocentrotus ('96) and by JANSSENS on the egg of Neapolitan 

 Arbacia ('03 and '04). Both the investigators obtained extraovates, 

 but did not succeed in getting multiple embryos. 



While at Naples I also tried some extraovate experiments on the 

 egg of Echinus, Arbacia and Strongyloceiitrotus with the view that 

 they might give interesting evidence in reference to the developmental 

 physiology of multiple embryos. Under the same treatment the 

 fertilization membrane of the first named form did not burst and con- 

 sequently no extraovates were formed. This is due, I think, to the 

 fact that in Echinus the space between the egg and the membrane 

 is so wide that the turgid egg does not reach the membrane while in 

 a hypotonic solution. In both Arbacia and Strongyloccntrotus I was 

 able to obtain extraovates. In using sea-water of various degrees of 

 dilution I found out that a mixture of sea-water 40 4- fresh-water 60 

 is the best for the present purpose. Eggs with extraovates, however, 

 failed to develop into double- or triple-plutei. The experiments, 

 therefore, were a failure as regards the above problem. Yet in- 

 cidentally they yielded a result worth recording in respect to elea- 



