THE AMERICAN NATURALIST [Vol. XL VI 



It is well known that an apparent confusion exists 

 among observations on hybrid Echinoid larva?, as to 

 whether plutei of a maternal type, a paternal type or of 

 mixed form are derived from certain crosses. Different 

 results have been obtained by different investigators and 

 by the same investigators working in different regions, 

 or in the same region in different seasons. 



From my own results I am convinced that there is no 

 reason for believing that any of these observations are 

 incorrect and that this dissimilarity of results may be 

 traced to the influence of the constitution of the sea water 

 at different times and places, to temperature, etc. 



If we look into the matter carefully we find that there 

 is a correlation between the fate of the maternal and 

 paternal chromatin and the character of the plutei. 



It is a remarkable fact that in the general literature of 

 genetics, authors who have noted the fact of elimination 

 of chromosomes, as shown by the researches of Baltzer 

 and Herbst, have not also noted their retention in some 

 cases, and the influences of ihis retained chromatin on the 

 character of the larvae. 



It may be seen, by the examination of Baltzer 's tabu- 

 lation, given in his 1910 paper, that in the cases cited an 

 elimination of presumably the introduced paternal chro- 

 mosomes is followed by a pluteus of the maternal type, 

 and that the retention of all the chromosomes may be 

 followed in some cases by a pluteus of a mixed or inter- 

 mediate type, in other cases by a pluteus of the maternal 

 type. To these cases I must add the case of the retention 

 of chromosomes followed by a pluteus of the paternal 

 type, this being afforded by the Hipponoe £ X Toocop- 

 neustes $ cross. 



In this instance we have a clear example of Hipponoe 

 dominance with respect to larval skeletal character, and 

 this dominance is correlated with the retention of Hip- 

 ponoe chromosomes. 



I have not asserted that every Toxopneustes egg which 

 is fertilized by Hipponoe sperm gives rise to a pluteus 



