24 DAVID H. TENNENT 



The short hook is definitely locaHzed, according to Baltzer, in the 

 egg (tej^t and diagrams, p. 579). The fact that it does not occur 

 in his figs. 16a and b nor in 17a, b and c harmonizes with this idea; 

 but when we turn to fig. 23a (Baltzer, '10) — Sphaerechinus 9 X 

 Strongylocentrotus d' — we find what might be interpreted from 

 the illustration as a short hook. The author definitely states 

 ('10, p. 509), that he has never found a hook-shaped chromosome 

 in Sphaerechinus. If both of these apparent hooks be such, one 

 of them must be the unpaired element seen in half of the straight- 

 fertihzed Strongylocentrotus eggs. It is also difficult to under- 

 stand why the elongated rods in the anaphase plates (Baltzer's 

 metaphase) in figs. 66, 76 and 11 ('09) should not be regarded as 

 long rods, as in Echinus (Baltzer 2a and b, 3a and b). My hesi- 

 tation in speaking of these possible interpretations is overcome 

 only by the fact that the conditions in the illustrations are similar 

 to division figures in my own material. 



The investigations of Heffner ('10) on Toxopneustes show that 

 this is in some respects like Strongylocentrotus. Heffner shows 

 for straight fertilized Toxopneustes eggs two Vs three Vs and 

 two long rods. The Vs may be regarded as comparable to the 

 hooks. The long rods in Toxopneustes are like the long rods shown 

 in Baltzer's figures of Strongylocentrotus. We need facts con- 

 cerning the chromosomes in many species of Echinoids. They 

 should be studied not only in straight-fertilized eggs, but in' 

 crosses, in chemically fertilized material and in fertilized enucle- 

 ated egg fragments. 



