18 DAVID H. TENNENT 



9 X Hipponoe d" cross ('11) showed that a hook-shaped chromo- 

 some was present in 50 per cent of the eggs and that it must 

 have had its origin in the paternal, i.e., Hipponoe, nucleus. I 

 shall proceed immediately to a consideration of the crosses. 



TOXOPNEUSTES 9 X HIPPONOE cf 



As a general comparison between the chromosomes of straight- 

 fertilized Toxopneustes eggs and those of straight-fertilized 

 Hipponoe eggs, it may be stated that in Toxopneustes the chro- 

 mosomes are more slender and less closely massed on the spindle 

 than in Hipponoe. The massing of Hipponoe chromosomes is 

 due, in part, t6 their larger size and the fact that the Hipponoe 

 egg and amphiaster are smaller than those of Toxopneustes. But 

 in spite of the fact that the Hipponoe chromosomes are larger, 

 when studied in straight-fertilized eggs, I have found it impossible 

 to distinguish in general between the chromosomes of the two 

 species in cross-fertilized eggs ; that is, I cannot find one group of 

 slender chromosomes and another group of thicker chromosomes, 

 which I can identify as of Toxopneustes and Hipponoe respec- 

 tively. In the cross-fertihzed eggs all seem to be of about 

 equal thickness. 



The chromosomes of the straight-fertilized eggs are in general 

 rod-like in form, some long, some short; in particular, a few have 

 individual peculiarity of form. These latter in Toxopneustes 

 (Heffner, '10) are either two Vs or three Vs and two long rods; in 

 Hipponoe (Pinney, '11) four Vs, or four Vs and a hook-shaped 

 chromosome. 



When we examine the mitotic figures of Toxopneustes 9 X 

 Hipponoe d" material (figs. 1-11) we may identify these elements 

 readily. In fig. 1, four Vs, a long rod, a hook and, in addition, 

 two other bent elements (fig. 1, C) which I have never found in 

 other division figures. Fig. 2, thre^ Vs and a hook. Fig. 3, three 

 Vs and a hook. Fig. 4 three Vs and a hook. Fig. 5 three Vs a 

 long rod and no hook. Fig. 6, two Vs in early anaphase. Fig. 7, 

 two Vs and no hook. Fig. 8, three Vs and no hook. Fig. 9, three 

 Vs and no hook. Fig. 10, two Vs. Fig. 11, three Vs and a hook. 



