CHROMOSOMES IN CROSS-FERTILIZED ECHINOID EGGS. I3I 



B. The Moira 6 Arbacia ? Cross. 



In effecting this cross the Arbacia eggs were allowed to stand 

 in sea water for seven hours, the water being changed every hour, 

 and then fertilized. The controls gave no segmentation. 



Cleavage began about forty minutes later ; again approximately 

 as in normally fertilized eggs, in both cases being slightly hastened 

 or retarded by variations in the temperature of the water. 



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% 



7 " 



V/ 



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Fig. 2. Arbacia egg X -Moira sperm. Egg outline omitted, otherwise drawn 

 to same scale and reduced as are plate figures. Chromosomes scattered throughout 

 cytoplasm. Arbacia chromosomes and Moira chromosomes may be distinguished 

 from one another by size. 



The sections of eggs of this cross are perhaps of greater in- 

 terest than those of the Moira-Toxopimistcs cross because of the 

 fact that the chromosomes of the two species are of sufficient 

 difference in form to be distinguished from one another. 



