224 WM. EEES B. ROBEKTSON 



figures 162, 186, and 187; and since the number is small com- 

 pared with that of other genera of the lily family (which possess 

 twenty-four), I believe that Trillium may possibly present a 

 case of compound chromosome formation similar to that of 

 Chorthippus. 



2b. Y-shaped chromosomes in somatic, spermatogonial, and 

 second spermatocyte divisions and in anaphases of first spermato- 

 cytes. Beginning, among animals, with nematodes, we find 

 Ascaris megalocephala to have in one variety, four; in the other 

 two chromosomes, which appear to be of the U type (Boveri, '88, 

 figs. 44b, 60, 61). The spindle fibers are attached not at any 

 one point but along the whole mid-region. The only indication 

 of constriction which has been figured is that of the first matura- 

 tion chromosome, shown by Tretjakoff ('04, fig. 7). 



In annulates the Schreiners ('06a, figs. 2, 6, 8-12) describe 

 V-shaped chromosomes of the U variety. There is a long narrow 

 constriction in the middle but no indication of segmentation 

 such as exists in Chorthippus or Trillium. In Nereis Bonnevie 

 ('06, pp. 62, 63) has demonstrated V-shaped, J-shaped, and 

 rod-shaped chromosomes in somatic cells. 



After an examination of the cell studies on Copepoda by 

 Riickert ('93), Haecker ('95, '02, '11), Lerat ('05), Krimmel 

 ('10), Braun ('09), and Matscheck ('10), I have come to think 

 that possibly a good deal of the confusion in respect to variation 

 in chromosome numbers, heterotypical mitoses, etc., has been 

 due to the presence of compound chromosomes of the form, 

 either of V's, bent rods or straight rods, possessing a segmentation 

 similar to that which I find in Chorthippus. Lerat ('05, figs. 

 25-32, 46-50) has shown that three types of chromosomes exist 

 in the copepods as in other groups of animals and in plants; 

 namely, straight rods with terminal attachment of fibers, bent 

 rods or V's with subterminal attachment of fibers, giving J's 

 or hooks, and V's with either median, or submedian attach- 

 ment of fibers. The occurrence of these three types of chromo- 

 somes, especially the straight-rod type, has been overlooked 

 by the other investigators of the group, though Matscheck in 

 his figure 8 gives one rod chromosome occurring along with 



