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 Bin Phrynotettix.' 
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 C; and C, in Phrynotettix, where, also, only two combinations, 
the same two, out of a possible three have been found. 
Robertson calls attention to the obyious 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. Ii this element is similar to C; 
of Phrynotettix, 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 C; and the unequal pair in Acridium, the 
same combination, 7. ¢., 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 C;, 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 
1 Since writing this I have had an opportunity to examine slides frcem some new Phrynotettix 
material collected during the summer of 1915 by Miss Carothers 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. 
