506 D. H. WENRICH 



two assumptions, namely, (1) that the number of chromosomes 

 for the Acrididae is constant (i.e., 23, diploid series) and (2) that 

 the 'achromatic bridge' or constriction at the apex represents 

 the point of union between two telomitic chromosomes joined 

 at their proximal ends. Were we to generalize on these as- 

 sumptions and apply them to Trimerotropis a difficulty would 

 immediately arise. In the first place, this form possesses the 

 number of diploid chromosomes typical for the Acrididae (23) 

 in spite of the presence among them of V-shaped members. 

 If we should assume that each of these V's represents two for- 

 merly separate rods, then the total number of rods in the indi- 

 vidual studied would be 34, as follows: for the 4 pairs of ate- 

 lomitic chromosomes, 16; for the 2 heteromorphic pairs, 6; for the 

 5 pairs of telomitic chromosomes, 10; and for the atelomitic acces- 

 sory, 2, This number (34) would be a radical variation from the 

 supposedly constant number of 23, and in other individuals the 

 number might be more (or less). As shown by Carothers ('17), 

 the range in number of rods on this basis could extend from 30 

 (individual no. 62) to 40 (individual no. 6). From the stand- 

 point of constancy in number, therefore, the V's in Trimero- 

 tropis should not be considered compound. 



On the other hand, if it .s to be assumed that the 'constric- 

 tion' is a criterion for the recognition of compound chromo- 

 somes, then the majority, at least, of the atelomitic chromo- 

 somes-in the individual studied would have to be considered com- 

 pound (plate 2). It is true that the assumption of a compound 

 nature for the atelomitic chromosomes of Chorthippus enables 

 one to recognize the number typical for the group (23), but a 

 similar assumption for Trimerotropis only causes a wide diver- 

 gence from the typical number which is already present. Per- 

 haps the way out of the difficulty may lie in the suggestion made 

 by Robertson ('16, p. 221) that there are two types of V-shaped 

 chromosomes, one type representing two rods joined at their 

 proximal ends and the other type a bent rod with spindle-fiber 

 attachment in a non-terminal position. 



On this supposition the typical Acrididian number may be 

 conserved by assuming that the atelomitic chromosomes of 



