THE CHROMOSOMES IN CROSS-FERTILIZED 

 ECHINOID EGGS. 



D. H. TENNENT. 



In experiments which I carried on during the summer of 1907 ' 

 crosses were made between several echinoids, namely, by the 

 fertilization of: 



1. The egg of the spatangoid Moira atropos with the sperm of 

 the sand-dollar Mellita pentapora. 



2. The &g^ of Moira with the sperm of the sea urchin Toxo- 

 pncustcs variegatus. 



3. The zgg of Moira with the sperm of the sea urchin Ar- 

 bacia punctidata. 



4. The &%g of Toxopneustes with the sperm of Moira. 



5. The &%^ of Toxopimistes with the sperm of Mdlita. 



6. The Q%g of Arbacia with the sperm of Moira. 



7. The &%g of Arbacia with the sperm of Mdlita. 



8. The z%^ of Mellita with the sperm of Moira. 



The work was undertaken primarily with the object of obtain- 

 ing material for a cytological study of cross-fertilized eggs and 

 secondarily for the purpose of making a comparison, based es- 

 pecially upon the character of the skeleton, between larval forms. 



In this paper I shall consider some of the earlier phenomena 

 exhibited, in brief, the prophases and early metaphases of divi- 



Moira c? , . . Moira c? 



sion, in two of the crosses, ( i), Yoxof^eust^ ^"^ (^^' Ai-bacia^' 



reserving the consideration of later stages, of the other crosses, 

 and a general discussion of the results for a latter contribution. 



The method of effecting the cross-fertilization was the exceed- 

 ingly simple one of allowing the eggs, after their removal from 

 the ovary, to stand for several hours in sea water, the water being 

 changed occasionally, and at the most favorable time, which was 



1 1 wish to express my thanks to the Hon. George M. Bowers, U. S. Commissioner 

 of Fisheries, for the privilege of working in the Beaufort Laboratory and to Mr 

 Henry D. Aller, director of the laboratory, for many courtesies extended to me. I 

 am also indebted to Dr. Bartgis McGlone for information regarding the artificial fertili- 

 zation of Moira eggs. 



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