No. 542] CHROMOSOMES IN ECHINOID LABV2E 



71 



in mind. The chief aim has been the determination of the 

 presence of the haploid number of chromosomes and of 

 the fact that auto-regulation does not occur. This is true 

 for results published as late as 1910. 



In my study of this material I have found thai all of 

 the eggs are alike, possessing among the others two V- 

 shaped chromosomes. 



In the fertilized enucleated egg fragments, two classes 

 are evident. Half of the spindles show two V-shaped 

 chromosomes in each anaphase plate while halt' show hut 

 one. I have no conclusive evidence for showing whether 

 we are dealing with an X chromosome or with A' and }' 

 chromosomes. Counts are decisive for either view, and 

 therefore valueless. I believe that this is a matter which 

 can be decided only by a study of the spermatogenesis 

 of these forms. 



For some reason there is a belief in the tradition that 

 in Echinoids the somatic number of chromosomes is 

 thirty-six and in one case eighteen. Counts of perfect 

 polar views of anaphase plates in Toxopneustes give the 

 numbers thirty-seven and thirty-eight, but even from 

 these I do not feel warranted in applying a sex formula. 



It will be noted that the number of V's does not agree 

 with our expectation from the straight-fertilized eggs. 

 I can only say that my description is of the facts as I 

 find them in my preparations. From this it would seem 

 that the number of V-shaped chromosomes in straight- 

 fertilized Toxopneustes eggs should be three and four. 

 These facts are further substantiated by conditions in 

 the Hipponoe X Toxopneustes crosses. 



The second point of which I wish to speak is that ol 

 correlation of chromosomes and larval characters. The 

 only larval structure which has a form sufficiently definite 

 to be used for comparison is the skeleton. The most ad- 

 vantageous forms for this purpose are those in which 

 the pluteus of one parent has skeletal arm rods of a 

 simple straight form and the other rods of the latticed 

 type. 



