54 
EDMUND B. WILSON 
classes having the peculiarities heretofore described). ^ Numbers 
above 22 arise through the addition of one or more relatively 
small ^'supernumeraries/' which agree in behavior with the small 
idiochromosome, of which they are probably duplicates. None 
of my own material (53 individuals, of three species) showed less 
than 22 chromosomes, and at least one small idiochromosome was 
present in all. In all of Montgomery's material of M. terminalis, 
however (9 individuals), this chromosome is absent, the sperma- 
togonial number is but 21, and the large idiochromosome appears 
without a synaptic mate as a typical odd or accessory chromosome. 
The foregoing results were based on the study of 62 individuals 
in all, representing the three species, terminalis, femoratus and 
granulosus. In February, 1909, I took at Miami, Fla., two addi- 
tional male specimens of femoratus, quite typical in structure, 
and closely similar in external appearance. One of these (No. 63) 
is an ordinary 23-chromosome form with one large supernumerary 
(like Nos. 13 or 48 of the general list given in ''Study V") and is 
only of interest for comparison with the other individual. The 
latter, hereinafter designated as "No. 64," shows a different 
chromosome-combination from any heretofore seen in this genus 
or elsewhere. The diploid groups (spermatogonia) contain 22 
chromosomes; but both these groups in themselves and their 
history in maturation proves most clearly that they are not the 
same as in the typical 22-chromosome forms, differing from the 
latter in respect to the idiochromosomes and the m-chromosomes. 
In the typical forms there are, as stated above, two of each of 
these chromosomes. In No. 64, on the other hand, there are three 
m-chromosomes and but one idiochromosome (the large), the 
latter appearing as a typical odd or accessory chromosome, as in 
the material of Montgomery; thus, 18 autosomes -|- 3 m-chromo- 
somes + 1 odd chromosome = 22. That this is the true interpre- 
tation of the facts is demonstrated by the behavior of these respec- 
tive chromosomes in the maturation-process. I would emphasize 
the fortunate fact that both testes of the animal show excellent 
fixation and staining (strong Flemming, iron haematoxylin) and 
that they contain multitudes of division-figures which demonstrate 
» Ibid: '056, 05c, '06, etc. 
