2O2 HAKI1ARA HEFFNER. 



known in Ascaris, and compound chromosomes are found in 

 the maturation mitoses of certain insects (McClung, '05, Payin-. 

 '09). In some of these latter cases (Payne, '09) the plurivak'iu 

 chromosome has a spindle fiber attached to each unit in the early 

 metaphase and in many cases two spindle fibers from each pole 

 are attached to one of each of the four units of a tetrad in primary 

 maturation mitoses (Stevens, '10). 



Since the Y-shaped chromosome of To \~opneustes seems to be 

 exactly comparable to the hook-shaped chromosome of Echinus 

 and StrongyJocentrotus, the question arose whether, assuming 

 that the V-shaped chromosomes of Toxopneustes may be biva- 

 lent, one might by careful observation be able to trace in the early 

 metaphase two spindle fibers from each pole attached to each 

 of them. As the spindle fibers were not especially clear in the 

 preparation stained with iron-ha?matoxylin alone, a few slides 

 were counter-stained with Rubin S. Among 42 cases I found 

 only two where I was inclined to count two fibers; in all other 

 cases I was certain that only one fiber from each pole was attached 

 to each V-shaped chromosome. My observations have there- 

 fore failed to add any facts supporting Baltzer's suggestion, 

 which, however, future investigation may verify. 



Baltzer ('090) traced the heterochromosome in Strongylo- 

 centrotus and Echinus to the female pronucleus. Unfortunately 

 I was not able to obtain suitable material for this purpose, but 

 further investigation will probably reveal the same conditions 

 as in Echinus and Strongylocentrotus. 



DISCUSSION. 



Comparing the chromosomes with peculiar shape in Echinus 

 and Strongylocentrotus with those in Toxopneustes we find that 

 the hook-shaped chromosomes in Echinus and Strongylocen- 

 trotus have no exact equivalent in Toxopneustes. The two ex- 

 tremely long rod-shaped ones are found in the three spr< -i< -. 

 The Y-shaped chromosomes in Toxopneustes are very similar 

 to the horseshoe-shaped chromosomes of Echinus in rrs|xrt to 

 their formation and the equal length of their two arms. They 

 differ from the Echinus chromosomes as already mentioiu-d in 

 their length and slender ness. As in Echinus we are n<>t aliK i.. 



