16 
PROCEEDINGS OF SOCIETIES. 
MacLeay, having been given only as a secondary one, may almost be left out 
of consideration, just noting, with regard to the larvae, that the alleged agree¬ 
ment with that order is not so near as with the Hymenoptera, or, still more, with 
the Diptera; while the appearance of rudimental wings and elytra in the perfect 
insect seems to be merely a notion. The group having been placed, as part of 
the order Diptera, in the sequence adopted by Burmeister, Siebold, and Schioedte, 
between the Neuroptera and Lepidoptera, I may glance at the partial similitude 
that subsists between it and the Physapoda in the mouth—both having lancet¬ 
like enclosed mandibulse, along with exterior palpigerous maxillae and a palpi- 
gerous labium; but, in reality, the agreement very much depends on our 
arbitrary selection of particular oral characters, the difference in other points of 
view being considerable, and the whole organization and embryology of the two 
groups is very dissimilar. With the Lepidoptera it seems scarcely necessary to 
enter into a comparison, and Duges has stated well enough all that he could find 
in favour of an affinity to the Hymenoptera. It is their relation to the Diptera 
which seems to demand the chief consideration; and such a relation is willingly 
admitted, notwithstanding some difficulties which may seem to forbid their 
reception into that order. The Diptera, like the Pulicidae, have a pair of palpi 
attached to the base of the maxillae, the latter consisting of a simple lobe, 
the basal part being analogically considered as abortive. The lancet-like condi¬ 
tion of the upper organs of the mouth is common to both, although in Diptera 
there are usually two central lancets—the labrum and hypopharynx, only one 
of which finds a representative in the Pulicidae. 
The distinctly formed labial palpi of Pulex present an obvious difference ; but 
this may not be of so great importance, if we suppose the structure and position 
of the palpi to indicate a tendency to coalescence, fulfilled in the geniculated 
sheath of the proboscis of Diptera; or if the development of the labium in the latter, 
at the expense of the total abortion of the palpi, be admitted, then Sarcopsylla pre¬ 
sents us with this last modification already accomplished. The contiguity of the 
legs of each pair, and the want of terminal spurs of the tibiae as distinguished in 
form from the other spines, and even the orderly distribution of spines or bristles 
upon the body, as well as the simple organization of the terminal segments, agree 
best with the Diptera. The pentamerous perfection of the tarsi is a character to 
which all the eminently flying orders (Anelytra) tend,* and only so far to be re¬ 
garded in this view, as it is eminently exhibited in the Diptera.f The general 
character of the metamorphosis is sufficiently near to the Dipterous group in 
which the larvae are peripneustic (Mycetophilidae, Bibionidae, Cecidomyzidae), 
the single pair of jaws (mandibulae), pair of antennae, pair of palpi, want of eyes, 
of feet, along with the mode of life and progression, agreeing better with these 
than with any other larvae that undergo a complete metamorphosis. This point 
I touch, and only touch on, because some authors, influenced by the similarity 
of parasitic habits, and what will perhaps be found, on closer consideration, a 
very imperfect analogy in the oral organs, have brought the Pulicidae near to 
the Coriaceae, the most remote point of the scale of Dipterous organization from 
* This characteristic appears to be as perfect in the Diptera as in the Lepi¬ 
doptera, although the function of flight degenerates completely in an aberrant 
group of the former order. Nay, in that very group there are seemingly traces 
of a further extreme subdivision of the joints of the legs, which may probably 
sugge st a remote approach to the Arachnida, such as popular language has 
stamped with the title of “ spider flies.” The Pycnogonidae in general, like the 
Nycteribidae, are epizoic wanderers ; but I do not venture to lay any stress on 
a relation of this extraneous nature. 
t The few exceptions to the pentamerous character of the Diptera which 
have been marked ( [Dicerafurcata , Echinomyia tetraumera, Monodicrana termi- 
nalis) rest on such limited, nay nearly individual observations, as urgently 
to call for a more general verification, and we may perhaps be allowed to hold 
them in suspense for the present. 
