STUDIES ON CHROMOSOMES 
75 
by the work of Stevens and myself, is widely distributed among the 
insects (Hemiptera, Coleoptera, Diptera) and is strictly confined 
to the male line (except when supernumeraries are present). In 
species having an odd or accessory chromosome the Y-element 
(small idiochromosome) is wanting, and I have urged this fact as 
showing that this latter chromosome cannot play any essential role 
in sex-production^^^ or in the transmission of the secondary sexual 
characters, as Castle ('09) ingeniously suggests. What I desire 
here to point out is that by parity of reasoning we should also con- 
clude that this chromosome is devoid of any special significance in 
heredity of any kind, at least as far as the visible external charac- 
12 instead of 11 separate chromosomes in the first spermatocyte division, as we do 
in the 22-chromosome individuals of Metapodius (Wilson: '09c). Throughout the 
Hemiptera, indeed, when the accessory chromosome (or its homologue, the large 
idiochromosome) is accompanied by a synaptic mate or Y-element, the two are 
separate in the first division, which accordingly shows one more than the reduced 
or haploid number — i.e., ^+1. The photographs of Foot and Strobell show, how- 
ever, 11 chromosomes in this division (the two m-chromosomes being of course 
counted as one, like the other bivalents), as they should if thesperraatogonial num- 
ber be 21. 
Still, this might be a case like that of Syromastes, where no Y-element is present, 
but the accessory is itself double — though such a parallel would hardly help the 
case, since in no form is the failure of the accessory to divide in one division more 
indubitably shown than in Syromastes, while Foot and Strobell are persuaded that 
it does divide in Anasa. But, secondly, my own extended additional observation, 
like the studies of Lefevre and McGill ('08), still continues to give but one result 
as before. The living animals (from the same locality as the material of Foot and 
Strobell) have been kept by hundreds in the greenhouse for months at a time in 
successive years, and have been regularly employed for class work in cytology and 
for experimental purposes, in the course of which large numbers of additional 
sections and smears have been prepared and examined. Others as well as myself 
have carefully searched among these preparations for cases showing more than 21 
spermatogonical chromosomes, without success apart from the double or multiple 
groups that occasionally appear. The same relation continually recurs, namely 
21 spermatogonial chromosomes of which three are larger than the others, while 
in the dividing ovarian cells the number 22 appears with equal constancy. That 
not even one case of 22 spermatogonial chromosomes has thus far been found is 
indeed surprising; for plus variations in the diploid groups are known to occur in 
some species of Hemiptera, and I have myself described such cases (e. g., Wilson: 
'09c). 
These and other reasons lead me to believe that the conclusions of Foot and Stro- 
bell were based on the observation either of very rare fluctuations in the normal 
diploid number or of accidental products of the technique. 
1" Loc. cit.: '06, '09a, '09d. 
