218 WM. REES B. ROBERTSON 



Baumgartner ('03) found in the field cricket (Gryllidae) twenty- 

 one chromosomes, whereas in the house cricket (Gryllis domesti- 

 cus) there were twenty-nine. His figures of the field cricket show 

 similar, though small, V-shaped chromosomes, whose apices are 

 turned inward (figs. 203, 204). By counting each of these V's 

 as two chromosomes, the number here also is twenty-nine. 



That my suspicion is well-founded in regard to V-chromosomes, 

 has just been shown by the work of one of my students, Miss 

 Woolsey, upon three species of Jamaicana (Locustidae) . Figures 

 194-201 have been taken from her paper (Woolsey, '15). One 

 species of this genus always has thirty-five (cf's) rod-shaped 

 chromosomes (fig. 194, spermatogonium). A second species 

 may have thirty-five (cf's) or thirty-four (cf's) chromosomes. 

 When the number is thirty-four, one large V-shaped chromo- 

 some is always present (spermatogonium, fig. 196, no. 14-16). 

 A third species shows either thirty-five rod-shaped chromosomes 

 or a group of thirty-three in which there are always two equal- 

 sized large V-shaped elements (nos. 14-16, fig. 200, spermato- 

 gonium). In prophases and metaphases of the first spermato- 

 cyte, individuals of the 35-rod type present seventeen rod- 

 shaped tetrads similar to those of Tettigidae, in addition to a 

 very large sex chromosome (18x, fig, 195). In the 34-chronio- 

 some individuals, where one V is present, the first maturation 

 division shows fifteen rod-shaped tetrads plus the sex chromosome 

 plus one long V-shaped chromosome (octad), which evidentl}' 

 represents the V-chromosome of the spermatogonium joined to 

 two of the rod-shaped spermatogonial chromosomes (14, 14-16, 

 16, figs. 197-199). Careful measurements of the length of the 

 limbs of the V in spermatogonia and first spermatocytes and of 

 the chromosome attached to the end of each limb of the V 

 in first spermatocytes show each limb to be of the same size as 

 the chromosome attached to it (figs. 198, 199). Each attached 

 chromosome (14, 16) is therefore probably homologous with the 

 limb of the V-type multiple chromosome to which it is joined. 



In figure 198 it is noticeable that one limb of the V is longer 

 than the other. In the pairing which takes place during the 

 first maturation, it is to be expected that the long limb will pair 



