DIPTERA, = UD 
seems to be entirely similar to that in the Melophagus larve#; at least Leuckart 
states that the old skin in these is shoved together toward the cephalic end of the 
larve, and there remains attached. The Hypoderma larva, immediately after the 
molt, is pure white, very soft, and appears naked, since the thorns do not become 
dark and distinctly separated from their surroundings until they harden. 
Three forms or stages are to be distinguished, corresponding to the molts, which 
forms in Hypoderma, Gastrophilus, and Dermatobia show great differences. In the 
third stage the larvze reach their full size, usually change their color, and that often 
very considerably, and then first leave their host animal, crawl away and pupate, 
after the manner of the Muscide. 
(7) This pupation must be considered as a third molting, in which, however, the 
skin is only detached around the pupa, but is not stripped off, and remains in con- 
nection with it by means of four trachee. The hardened larval skin, or puparium, 
is burst open at the cephalic end by the emerging fly by means of the frontal bladder 
filled with flnid, in the direction of the arcuate sutures inadouble manner. Although 
the pupation resembles herein that of the Muscidz in general, yet there occurs in 
one part of the (stride, i. e., in Hypoderma, a peculiarity which has not been 
observed before, namely, that the larva transforms in the puparium in a completely 
outstretched condition, and this, therefore, is far larger than the insect which comes 
forth from it. 
(8) So far as they have been observed, they lead a parasitic life in mammals, and 
feed upon the juices of these animals. In Hypoderma, a blood-red intestine often 
shows through, and it is likely that these sometimes suck up blood in addition to 
the exudation which immediately surrounds them. 
(9) The closely observed larvz all show at first a slow and finally a rapid devel- 
opment, so that there occurs a resting stage, which often lasts seven months, betweer 
the swarming of the imago and the first visible appearance of the larve. 
The larve of the (stride were formerly divided into two groups—into larve 
with oral hooks and those without external mouth parts. Such a separation is of 
service in distinguishing the full-grown larve, but scientifically unnatural and 
incorrect, since in the first place this peculiarity of the full-grown larve corre- 
sponds to no similar degree of relationship of the perfect insects, and in the second 
place it is ouly temporary (p. 39), since all cstrid larve possess oral hooks when 
they are quite young. Such a division also as Clark attempted to make into cari- 
cole, cuticole, and gastricola, is inadequate, for while the species of a genus do, 
indeed, always agree in life history so far as their occurrence as parasites in a deter- 
minate organ is concerned, nevertheless the larve of very different genera may also 
share this same manner of life with others; for instance, Hypoderma, Cuterebra, 
Dermatobia, among which there is far more difference between one and two than 
between Cuterebra and Cephenomyia, if the imagoes are considered. Such a divi- 
sion is, therefore, likewise not a natural one, since it disturbs the natural relations 
of affinity. Two elements must be considered in order to bring about an approxi- 
mately natural division: In the first place, the organization of the larve, and, in the 
second place, their manner of life, and the latter in a subordinate degree, though 
this is here more important than in other animals, since as yet there is no example 
of two species of (Estridie of one genus having been found parasitic in different sys- 
tems of organs. Thus the Cephenomyia larve belong to the wsophagus, the Cepha- 
lomyia and (Estrus larve to the nasal and frontal cavity, those of Gastrophilus to 
the intestinal tract, and those of Hypoderma to the subcuticular cellular tissue. 
Although it is stated that the larva of Gastrophilus has been found in the csoph- 
agus, this is one of the exceptional cases which are not authenticated. Of course, 
only the full-grown larva is meant here, since young larve may always be found in 
other places during the immigrations. So, for instance, the young (Estrus and Cephe- 
nomyia larve both immigrate in like manner through the nose, and their roads do 
not separate until they get there, but the former migrate into the frontal cavity and 
the latter into the @sophageal cavity. 
