20 DAVID H. TENNENT 



in the Hipponoe egg and furnishes corroborative evidence that our 

 conclusion reached in the second statement is correct. 



Our analysis has given conclusive evidence that in Hipponoe 

 there is a heterochromosomc which is of paternal origin. This 

 evidence is of value since it indicates that the conclusion drawn 

 from Baltzer's ('09) investigation, which is supported by the work 

 of Heffner ('10), i.e., that in Echinoids the female is the hetero- 

 gametic sex, while the male is homogametic, is not of general 

 appHcation, and that in one Echinoid at least, Hipponoe, we have 

 conditions which are similar to those found in insects. 



THE BEHAVIOR OF THE CHROMOSOMES IN CROSS-FERTILIZED 



ECHINOID EGGS 



A very different phase of my work is concerned with the idea 

 of the fate of the chromosomes in these crosses and the correla- 

 tion of this behavior with the environment. 



Baltzer ('09, '10) and Herbst ('09) have shown the fact of chro- 

 mosome elimination in various crosses. Baltzer ('10, pp. 608-609) 

 has given a valuable tabular summary of facts in Echinoid 

 crosses, with the character of the resulting pluteus. In most 

 instances chromosome ehmination is followed by a maternal 

 pluteus and chromosome retention is followed by an inter- 

 mediate pluteus. In two crosses, however. Echinus 9 X Antedon 

 cT and Strongylocentrotus 9 X Antedon d", there is no ehmination, 

 and the skeleton of the pluteus is maternal in character. 



In other crosses, Strongylocentrotus 9 X Echinus & and Sphae- 

 rechinus 9 X Arbacia d", there is no elimination and a 'maternal 

 intermediate' pluteus results. 



For the crosses under consideration in this paper I have pre- 

 viously shown ('10, '11) that the plutei resulting from the cross, 

 no matter in which direction the cross has been made, have a 

 skeleton which resembles that of the Hipponoe pluteus more 

 nearly than it does that of Toxopneustes, and I have stated that 

 as a result of this cross we have a Hipponoe dominance with 

 respect to the character of the skeleton. This dominance is 

 not complete and in many instances the skeleton is of a ' Hipponoe 

 intermediate' type. 



