226 WM. EEES B. ROBERTSON 



region of the chromosome, but must appear and disappear with 

 the hfe cycle of the animal. He looks upon it as the point of 

 conjugation of two homologous chromosomes, the halves of the 

 rod (limbs of the V) being homologous chromosomes and, of 

 course, equal in length. That this is not the case, is shown by 

 the fact that the limbs of the V are frequently of unequal length 

 (Lerat, '05), as in Chorthippus and in so many species with V- 

 shaped chromosomes. 



The variation in chromosome numbers which Krimmel (^10) 

 found in somatic mitosis of Diaptomus — between twenty- 

 eight and fourteen (reduced number) — Haecker ('11, p. 113) 

 explains as follows: "Man wird die intermediaren Zahlen auf 

 einen unvoUstandigen Zerfall bivalenter Elemente, also auf 

 eine Mischung bivalenter and univalenter Elemente zuriickfiihren 

 diirfen." Haecker is probably right in ascribing numerical 

 variation to breaks at points of segmentation, though I believe 

 he is wrong in thinking that the 'univalent' chromosomes mak- 

 ing up these 'bivalents' are to be considered as members of 

 homologous chromosome pairs. 



Schiller ('09, figs. 7-9) describes tetrads in somatic cells of 

 Copepoda. He probably saw some of these compound chromo- 

 somes with transverse segmentation in which the longitudinal 

 split is visible, as in Trillium (Gregoire et Wygaerts, '04, fig. 

 20). In such a chromosome one might see four parts and thus 

 mistake it for a tetrad (compare fig. 134). 



Among the insects V-chromosomes have been found in the 

 phasmids by de Sinety ('01) ; in five acrididaean genera; in Steno- 

 bothrus by de Sinety ('01), Davis ('08), Gerard ('09), Meek (10', 

 '11, '12) and myself, in Hippiscus, Mermiria, Hesperottix, and 

 Chortophaga by McClung ('05, '14); in the Locustidae by Wool- 

 sey ('15), Stevens ('12), McClung ('05), Buchner ('09), Vejdovsky 

 ('11-12), Davis ('08); in the GryUidae by Baumgartner ('04) 

 and Payne ('12) ; and in Coleoptera (Coptocycla) by Nowlin ('06). 



In the phasmid Leptynia attennuata Pant., de Sinety shows in 

 spermatogonia (figs. 73, 75) three V's among thirty-six chromo- 

 somes. In Stenobothrus three pairs of V's, such as I have found, 

 have been described by all authors who have investigated this 



