a 
1914} A Structural Study of Caterpillars. 117 
until they separate, then forks, in the substance of the very 
slightly developed ventral diaphragm and runs out, often 
along the incisure, to the spiracle and from there to the tip of 
the wing of the heart; no muscles overlie its main stem, but 
it sends down branches to anastomose with the second nerve, 
and connects with the anterior one in the neighborhood of the 
spiracle. It certainly supplies the spiracle and probably some 
muscles, but on account of the anastomoses it is impossible to 
be sure. Sometimes the fusion of the connectives is complete, 
as in Sphecodina (Plate 5) and this nerve seems to arise from 
the anterior end of the ganglion after the one to which it 
belongs. In the thorax its connections are always perfectly 
clear, because of the wide separation of the connectives. 
On the third to sixth segments the structure is identical, as 
described, except for purely individual variation, but the others 
show various stages of reduction. 
OTHER SEGMENTS OF THE ABDOMEN. 
The second segment differs only in the reduction of the 
muscles of the proleg, and the loss of a couple of fibres, but 
they do not change their points of insertion. x is insignificant 
or absent; k and p are usually unchanged, but may appear 
as short parallel oblique fibres evidently homologous to I and 
L dorsally. This condition appeared in an odd specimen 
of Malacosoma disstria. y, m, n, q and r are reduced in 
strength, but not notably changed in points of insertion. 
In the first segment the proleg is so reduced as to be unrecog- 
nizeable, in a stage corresponding to Berlese’s Fig. 477 D, 
which was evidently prepared from the seventh segment. 
The fat pad, which causes the proleg of the second segment 
to keep nearly its normal relations, is unimportant here, and 
the transverse fibres (of the 1, q group) are shortened. 8, 
(representing y) is merely a couple of fine fibres which barely 
cross the fold. The antecosta dorsally and precosta ventrally 
are also not developed and the muscles which normally end 
in them are continued to the front of the segment; these are 
a, i, E and f’ when present. As the trunk trachea disappears at 
the first spiracle a is not distinguished from @, whose fibres 
are crossed as a result of the moving forward of E and F. 
H, however, may remain unchanged, and the spiracle is only 
