CHROMOSOME STUDIES 265 



that tetrad does not always do so, as may be seen in cells 5 and 

 6 of this table. 



While the behavior of chromosomes in forming tetrads is not 

 always constant, as Moore ('06) and Baumgartner ('04) be- 

 lieved, but only tends that way; their behavior, on the contrary, 

 in either forming or refusing to form certain associations result- 

 ing in compound chromosomes seems to be constant in some 

 cases (Jamaicana subguttata), only for the individual, in others 

 (Drosophila ampelophila) for the species or in still others (Chor- 

 thippus, Syrbula, Hesperotettix, Mermiria) for the genus. 

 In Chorthippus curtipennis, for example, there are present in 

 all individuals of the species so far examined three pairs of Vs. 

 These pairs of V's may be distinguished and recognized by 

 the relative lengths of the two arms, which differ enough to 

 enable one to recognize the V's individually, not only in all cells 

 of this species, but — judging from figure 6 of Meek ('12b) and 

 those of Gerard and of Davis — in other species of the genus as 

 well. The lengths of these arms in Chorthippus are almost 

 identical with the relative lengths of the nos. 5, 7, 8, 9, 10, and 

 11 chromosomes in Syrbula, a nearly related genus, in which 

 no V's are formed. The behavior of these pairs, so far as our 

 knowledge goes, is therefore constant within one genus (Chorthip- 

 pus) in forming V's, and in another genus (Syrbula) in not form- 

 ing V's. The same may be said of the sex chromosome and the 

 particular autosome with which it forms a compound (V-chromo- 

 some) in the species of Hesperotettix, when compared with their 

 behavior in failing to do so in the majority of other genera. 

 Likewise in Mermiria, and especially in the four large pairs of 

 rod chromosomes in Drosophila, as Metz has shown, where in 

 one type of species they remain independent rods, in another 

 type two pairs of the rods unite to form a pair of V's, while 

 in a third type the four pairs of rods unite to form two pairs 

 of V's. 



Individual, or at least genetic, continuity and specificity is 

 shown in chromosomes that are traceable. In the Tettigidae 

 the fact that we may trace and recognize any particular pair 

 of autosomes from the no. I's to the no. 6's, as well as the sex 



