220 WM. REES B. EOBERTSON 



to it — the Oedipodinae and Acridiinae — had up to this time been 

 thought to be twenty- three. As a result of the comparisons of 

 chromosomes in this genus with those of the related genus Syr- 

 bula and with those of some of the Oedipodinae and Acridiinae, 

 and in view of what I have found to be true of chromosome num- 

 bers and sizes among the genera of the Tettigidae, and especially 

 in the light of the relation known to exist between rod- and V- 

 shaped chromosomes in three species of Jamaicana, I am con- 

 vinced that the smaller number in Chorthippus is due to the 

 presence of Vs. I am reasonably certain that these V's, such 

 as we find in Chorthippus and Jamaicana and possibly in other 

 locustids and gryllids, have resulted from the linkage proxi- 

 mally of two non-homologous chromosomes, and that the non- 

 chromatic bridge at the apex of these V's, — sometimes accom- 

 panied by a constriction, — from which the spindle fiber springs, 

 is the point at which this linkage has taken place. With these 

 conclusions in mind, I turn to a consideration of V-shaped and 

 segmented chromosomes described by others, and the possible 

 relation of such chromosomes to some of the problems of cytol- 

 ogy and genetics. 



V-shaped chromosomes are common in both plants and animals. 

 They are referred to in cytological literature as 'equal armed' 

 and 'unequal armed' (caudes) V's or U's, or as being 'hook- 

 shaped' or 'J-shaped' (Gregoire, '05, '10). The spindle fiber 

 springs from the apex of the angle formed by the arms and is 

 referred to as coming from the median, a near-median (inter- 

 mediate), or a subterminal region. Besides these V's, the only 

 forms of chromosomes we have, except in first-maturation divi- 

 sions, are straight rods and, possibly, spheres. In the straight- 

 rod type the spindle fiber usually springs from the end and is 

 spoken of as terminal. However, in Copepoda, where the 

 rods show transverse segmentation, the attachment of the fiber 

 may be median or sub-median. But in anaphases such rods 

 appear as V's and therefore may be so classed. For convenience, 

 I use the term V-chromosome in a general sense to include 

 all of these two-armed chromosomes, viz., the V's, U's, and J's, 

 and transversely segmented rods. However, I do nqt consider 



