M. E. MacGtKegok 
185 
Stomoxys calcitrans Linn. (Text-fig. 3 b.) 
In larvae of this fly the “ rings ” of the stigmal plates are, roughly, 
triangular in shape with the adjacent sides straightened and parallel. 
The “ button ” is relatively very large, and heavily chitinised, and 
situated near the middle of the plate. On three sides of the “ button,” 
and at right angles to one another, are the three sections of what may 
be regarded as the broken convoluted chain, with an S-shaped con¬ 
figuration, and very clearly defined. Each section of the chain is 
crossed throughout its length by a branching bar system similar to that 
seen in the other types of stigmata, except that in this case the bars are 
exceedingly slender, and though they can be vaguely made out under the 
higher powers of the microscope objective and X 5 ocular), it needs 
the very highest combinations (j 1 ^ oil imm. objective and X 12 ocular), 
to resolve them clearly. Under a magnification of 1440 diams. the bar 
system can be seen to consist not, as in the stigmata of Lucilia caesar, 
of a single line of branching rods, but of a series of rods in more than 
one plane which thus produce a most complicated network, the interstices 
of which measure only a few microns across. The general appearance 
of the stigmata of Stomoxys calcitrans nevertheless, even at low magni¬ 
fications, is quite characteristic, and cannot easily be mistaken for any 
other. The measurements of the stigmata are as follows : distance 
between “ buttons,” 0‘22-0‘26 mm.; breadth across plate, 0'28-0'30 mm. 
Haematobia serrata Desv. (Text-fig. 3 a.) 
Of all the forms described in this paper this has yielded the least 
definite anatomical data ; for two reasons: first, that the chitinous 
“ ring ” and stigmal plate generally are so heavily chitinised, that 
mounted in the manner described they are almost opaque to transmitted 
light under the microscope, except at irregular spots ; and secondly 
that owing to scarcity of material I have not been able to make a 
sufficient comparative study. That this form of stigmata belongs to 
the ptychotreme-type there can be no question, however, because by 
careful manipulation and focussing of the microscope the convoluted 
chain can be traced over its whole length, while it is very clearly seen 
at the irregular spots mentioned above where the chitin of the plate is 
not so thick. That the chain lies well above the heavier chitinous 
structures of the plate, as with the other stigmata belonging to the 
ptychotreme-type, is particularly well seen in this larva, for it is situated 
Parasitology vn 
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