WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. 121 



only two individuals, all the others showing a pair both members of 

 which were equal to the larger member of the unequal pair. The third 

 possibility, an equal pair, homologous to the smaller of the dyads, 

 was not found. This case is analogous to that of B in Phiynotettix.^ 

 In Acridium, Robertson found two individuals, one a male, the other 

 a female, possessing an unequal pair of chromosomes, whereas all the 

 other individuals studied showed the homologous pair to be equal, 

 both members being equivalent in size to the smaller of the two 

 members of the unequal pair. This case is analogous to those of 

 tetrads Ci and C2 in Phrynotettix, where, also, only two combinations, 

 the same two, out of a possible three have been found. 



Robertson calls attention to the obvious possibility of a loss of 

 chromatin from the unequal pair in Tettigidea, and suggests that the 

 loss of Mendelian factors could be accounted for in this way. He also 

 suggests that the loss of the distal ends of both the chromosomes, 

 resulting in a pair of small dyads each equivalent to the smaller mem- 

 ber of the unequal pair, might result in lethal conditions, or might 

 mean the loss of factors necessary for development. In the case of 

 the unequal pair in Acridium, he assumes that there has been an addi- 

 tion to one member of the smaller pair. If this element is similar to Ci 

 of Plu*ynotettix, as it seems to be, then the simpler explanation would 

 be that a part had been lost, just as in the case of the one in Tettigidea. 

 It is curious that in both Ci and the unequal pair in Acridium, the 

 same combination, i. e., a pair both members of which would be equal 

 to the larger member of the unequal pair, is lacking. I am inclined 

 to believe, if sufficient material were available, that the remaining 

 possible combinations would be found. The matter could, at least, 

 be tested by experiment. It is the hope of the writer to conduct 

 breeding experiments with this object in view. 



One further point remains to be considered in relation to chromo- 

 some-pair C. I have described these tetrads in detail elsewhere 

 (p. 85), but a reference to figure 107 (Plate 9) will recall that there 

 are three types, which I have designated as Ci, C2, and C3. If similar 

 types exist in the female, — Robertson ('15) found an unequal pair in 

 a female of Acridium, — and random mating be assumed for the ani- 

 mals possessing the three different types, then one ought to obtain in 



* Since writing this I have had an opportunity to examine slides frcn some new Phrynotettix 

 material collected during the summer of 1915 by Miss Garothers of the University of Pennsyl- 

 vania. In some of the individuals of the new material I have found the expected third type of 

 chromosome-pair B composed of two elements both equivalent to the shorter member of the 

 unequal type. 



