14 
PROCEEDINGS OF SOCIETIES. 
as a scutellum, but which, with Lacaze-Duthiers, I would refer to the 
abdomen. The presence of a spiracle on the lateral lobes seems conclusive 
as to the character of these parts. The comparative freedom of the edges is 
probably accommodated to the play of the muscles in leaping. The lateral en¬ 
largement of the mesopleurse is much less conspicuous, and has not nearly so 
much the appearance of a free process, which could be assimilated to an unde¬ 
veloped wing or elytron. 
The larva of the flea has been so well described already that there is little to 
add with regard to external form. (See Vol. II., pi. 4, fig. 3, 4.) The mandibles, 
first clearly demonstrated, as to their position in situ, by Mr. Westwood, work 
as nippers within the fleshy cavity of the mouth, and must be extracted in order 
to gain a clear idea of their form. They appear then wedge-shaped, but slightly 
incurved, ending with five minute teeth along the internal edge of the tip. (Fig. 
18.) The palpi are two-jointed, the first joint very short, the second nearly 
cylindrical, crowned at the tip with three tubercles. (Fig. 16, 17.) The inser¬ 
tion of each palpus is in a fleshy protuberance, forming jointly two lobes, sepa¬ 
rated in the middle by a stricture. (Fig. 12.) Behind them there is a soft, 
retractile wart, characterized by Degeer as a help to progression, the place of 
which is marked in figure 10 by the two minute hairs. In this place I have seemed 
to see a pair of exceedingly minute palpus-like tubercles, which, however, were 
again resolved by more accurate adjustment of the microscope, so that the ap¬ 
pearance was probably an ocular deception, such as frequently occurs about the 
origin of a hair. It is worth observing, however, that some unpublished draw¬ 
ings, which Mr. Westwood kindly communicated, represent this pretty much as 
I at first viewed it. The antennae, about twice as long as the palpi, are com¬ 
posed of two joints, and a crowning bristle ; the first joint is stout, emerging but 
little, and is surrounded by a ring of eight globular tubercles.* The second joint is 
nearly cylindrical, tapering a little, and about four times as long as the terminal 
bristle. (Fig. 14,) The depressed subcylindrical body is composed of twelve 
segments, each surrounded by a whorl of long hairs. The last segment is nearly 
twice as long as the preceding, and having three such whorls is consequently 
represented by two segments in Cestoni’s figure ; its posterior declivity is fringed 
above with finer hairs (Fig. 21, 22), and terminates below on each side with a 
slightly hooked horny process, which serves as a sort of foot. (Fig. 21, 23.) 
The integuments seem smooth and glossy, except under a high magnifying 
power, when a system of fine ambient striae may be detected. (Fig 19, 20.) 
At each side of the intermediate segments, a little before the middle, is a finely 
reticulated round space, adjacent to an oval spiracle. (Fig. 20, s.) Through 
the transparent skin a double trunk of extremely fine tracheae (t) may be detected 
running longitudinally, and connected by a cross branch half way between the 
spiracles, to each of which a stouter branch runs directly from the upper trunk. 
The number and arrangement of the spiracles I did not determine quite to my 
satisfaction, but have set it down as probably a prothoracic pair, and a pair in 
each of the abdominal segments except the last, that is nine pair, or, perhaps, 
only eight in all. The skin of the larva is sufficiently transparent to discover 
the course of the intestinal canal also; the slender oesophagus, and the small 
crop marked out by the sanguine colour of the contents, occupying a little more 
than the first two segments after the head, while the stricture which marks the 
passage of the small intestine into the rectum lies in the penultimate segment. 
(Fig. 4.) The whole alimentary canal (Fig. 7) is not much longer than the body, 
so that the small intestine alone is convoluted. The very slender oesophagus (e) 
is little longer than the head; the ventricle (v), including the crop, which is not 
limited by any external stricture, though the different colour of the contents 
indicates an internal partition, is nearly half the entire length ; the small intes¬ 
tine (t) and the rectum (r), each about half as long as this, the latter with a slight 
* The eye described and figured by Boesel, close to the base of the antenna 
in the larva, was probably the outermost of these tubercles, relieved in outline, 
and exaggerated by an imperfectly defining high power of object glass. 
