132 W. R. B. ROBERTSON 
ADDENDUM 
After this paper was worked out, a treatise by Miss Carothers 
(13) appeared, describing unequal tetrads in three species of the 
23-chromosome grasshoppers, Brachystola magna, Arphia sim- 
plex, and Dissosteira carolina. [ wish to consider her paper 
briefly here. | 
In the twenty specimens of the three species examined she 
finds the members of one of the three pairs of small chromosomes 
always unequal in size. The unequal pair occurs in spermato- 
gonial, in first spermatocyte and (separated) in second spermato- 
cyte cells. The members of the unequal pair agree with those I 
have found, in that they become separated from each other dur- 
ing the first and not during the second maturation division. This 
is evidence again that the first maturation division is the reducing 
division. [In their passage to the second spermatocytes these 
unequal members (diads) agree with those of my material in 
that they are distributed to these cells irrespective of the presence 
or absence of the sex chromosome. In this respect our unequal 
pairs differ from those of Gryllotalpa, described by Payne (712), 
where the longer chromosome was always accompanied by the 
sex chromosome in the anaphase of the reduction division. 
Payne may have been dealing with a group of sex chromosomes 
similar to what he has already worked out in another order of 
insects (’09). 
Miss Carothers’ material differs from mine, however, in that 
‘she finds the unequal pair present in every animal. I cannot 
agree with her in this respect, in Acridium or Tettigidea, as my 
drawings have shown. Possibly further search will show that 
the unequal pair is not always present in the species upon which 
she has worked. If this should be the case, the hypothesis of 
selective fertilization which she advances would be unnecessary. 
So far as Tettigidea and Acridium are concerned, it is not nec- 
essary to postulate selective fertilization. 
In thinking that the great number of combinations of chromo- 
somes possible is sufficient to account for all variations, I fear Miss 
Carothers may be mistaken. Gates (’09) has shown that in 
