THE BEHAVIOR OF THE CHROMOSOMES IN CROSS 

 FERTILIZED ECHINOID EGGS^ 



DAVID H. TENNENT 



Bryn Mawr College 



* 



TWENTY FIGURES IN TWO PLATES 



It is my purpose to present in this paper some of the facts 

 gained by a cytologieal study of Echinoid crosses gind to consider 

 critically the results of Baltzer and Herbst in similar studies. 



In my first work on the chromosomes of cross-fertilized Echi- 

 noid eggs ('08) I found that beyond the mere determination 

 of species differences in chromosomes, little could be done until 

 a careful study of the chromosomes of the parent forms, in all 

 phases of mitosis, had been made. 



Since that time important investigations on the straight- 

 fertilized eggs of some of the parent species have been completed 

 by two workers in my laboratory, Dr. Heffner ('10) and Miss 

 Pinney ('11) so that we are now prepared to identify somewhat 

 adequately the chromosomes in Toxopneustes X Hipponoe, 

 Toxopneustes X Moira, Arbacia X Moira and Arbacia X 

 Toxopneustes crosses. In addition we now have the important 

 studies of Baltzer ('09, '10) and Herbst ('09) on European forms, 

 for comparison. 



During the past year I have investigated reciprocal Toxo- 

 pneustes X Hipponoe crosses made in normal sea water and the 

 same crosses made in sea water whose alkalinity had been reduced 

 as described in my papers of 1910-1911. 



Heffner ('10) showed for Toxopneustes long rods and two Vs 

 or three Vs. Pinney ('11) showed for Hipponoe four Vs in all 

 eggs and in addition a long armed V, or hook shaped chromosome, 

 in half of the eggs. My own observations on the Toxopneustes 



1 Prepared for The Whitman Memorial Volume, but received too late to be 

 included. 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 1 



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