STUDIES IN CYTOLOGY 
I. A FURTHER STUDY OF THE CHROMOSOMES OF TOXOPNEUSTES 
VARIEGATUS 
Il. THE BEHAVIOR OF THE CHROMOSOMES IN ARBACIA-TOXO- 
PNEUSTES CROSSES 
DAVID H. TENNENT 
From the Zoélogical Laboratory, The Johns Hopkins University 
TWENTY-ONE FIGURES 
I 
In 1910 Miss Heffner made a study of straight fertilized Toxo- 
pneustes eggs and reached the conclusion that there were two classes 
of zygotes, one with two and one with three V-shaped chromo- 
somes in each anaphase plate. This condition showed a simi- 
larity to the one described by Baltzer (’09) for Echinus and was 
regarded as an indication that its significance was the same, 
namely that in Toxopneustes there were two kinds of unfertilized 
eggs. ; 
My observations on Hipponoé crosses (’11—’12) taken in con- 
nection with those of Miss Pinney (11) on straight fertilized 
Hipponoé eggs led me to believe that possibly there might be 
another interpretation for Toxopneustes and it occurred to me 
that the facts might be determined most readily by studies of the 
chromosomes of the egg in chemically fertilized eggs and of the 
chromosomes of the spermatozoan in fertilized enucleated egg 
fragments. The question to be decided was whether the un- 
paired V in zygotes containing three V-shaped chromosomes, was 
to be associated with the egg or with the spermatozoan. 
The work upon which this paper is based was begun in the Laboratory of the 
Bureau of Fisheries at Beaufort, N. C. I am indebted to the Hon. George M. 
Bowers, Commissioner of Fisheries, for the privilege of working in this labora- 
tory and to Mr. Henry D. Aller, Director of the laboratory, for many courtesies. 
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