PROCEEDINGS OF SOCIETIES. 
13 
to make some further examination, with a view to supply the deficiency. Not 
being likely to have leisure to resume the inquiry more systematically, it has 
been thought it might be as well to put on record the additional data obtained, 
however imperfectly elucidated, for the assistance of others, until some compe¬ 
tent anatomist may condescend to turn his attention to this neglected subject. 
For the materials of this investigation he has been chiefly indebted to Mr. 
Westwood ; and not less, for bibliographical information, to his Modern Classi¬ 
fication of Insects—a storehouse of entomological knowledge, which nearly dis¬ 
penses with the private labour of such research up to the time of its pub¬ 
lication. 
In entering on this inquiry, the following parts of the subject were considered 
to be so well established as to require no particular investigation. The history 
of the metamorphosis, the external form, and the oral organs in general of 
the larva, as well as of the perfect insect, the structure of the antennae and legs, 
and the segmentation of the abdomen. As points contested or imperfectly 
determined, there remained the exact composition of the labial palpi, and the 
analogical significance of the middle lancet of the sucker and of the lateral plates 
of the mesothorax and metathorax. No information, except that already quoted 
from Leeuwenhoek, was found extant as to the internal anatomy of either larva 
or perfect insect, or the outlets of the respiratory system. 
In Pulex cams the labial palpi were observed distinctly 4-jointed, and the 
membranous edge, figured by Curtis and Duges, by no means obvious, although 
the parallel direction and close contiguity of these palpi gives them the appear¬ 
ance of a simply articulated sheath, and suggests a tendency towards their co¬ 
alescence in such a shape, which indication, however, the abortion of the palpi 
in Sarcopsylla may be considered to neutralize. Duges’ observations, coupled 
with the general analogy of the antecedent and superior development of the 
labrum in insects, seem to fix this character on the middle lancet, although Grube, 
from the result of Gerstfeldt’s recent observations, has again treated it as a 
tongue or epipharynx.* The spiracles were found without difficulty in the per¬ 
fect insect, although they have been passed over without notice in general, and 
their absence even assumed by implication. In the abdomen they are segmen¬ 
tary, and placed in the upper half ring of each of the first six complete segments, 
in the anterior horny portion, a little in advance of and above the lower termi¬ 
nation of the comb, or row of bristles, and rather concealed by the overlapping 
of the thinner edge of the preceding segment. They are of moderate size, 
embraced by a circular horny ring of a dark colour, and the tracheae which arise 
from them can be seen through the transparent shield so plainly that both its 
spiral fibre and two stout trunks springing from it in opposite directions, at a 
little distance from the spiracle, are evident.f The first dorsal half ring, which 
wants a corresponding ventral piece, in consequence of the lateral prolongation 
of the metathorax, is also destitute of a spiracle ; but close under the sides of it, 
near the upper margin of the lateral lobe of the metathorax, is a similar one. 
The spiracles of the remaining pair differ in being closed externally by an annu- 
larly striated membranous cone, projecting from within the horny ring.J The 
spiracle is placed in the lowest part of the mesothoracic pleura, immediately 
above the hinder angle of the base of the intermediate coxa, and in a nearly 
membranous and thus apparently intersegmentary space. Between the protho¬ 
rax and mesothorax no spiracle was detected, although the examination may not 
have been sufficient to negative positively the presence of such. The squameous 
enlargements of the pleurae of the metathorax, which have been considered as the 
rudiments of wings, have quite the character of the rest of the integuments, and 
are similarly furnished with bristles disposed in two additional rows, nearly conti¬ 
nuous with the two upon the small dorsal half ring, which has been considered 
* Wiegmann’s Archiv fur Naturgeschichte. a.d. 1854. Bd. 1. 
t Plate 1. fig. 1. The half-ring inverted. 
X Plate 1. fig. 2. The remaining references are to Plate 4 of vol. 2. 
VOL. III. 
