DIPTERA. | te 
they are very different among themselves, and in part also in our defective knowl- 
edge of the muscid larve. 
At present, it is true, no real muscid larve are known with large thorn-warts—as 
I will call the dermal formations which occur in many cestrid larve, which are con- 
ical, soft at the base, fleshy, and corneous at the tip—also none with the character- 
istic stigmatal plate of the Gastrophilus larve; on the other hand, very many are 
known with thorns, like those of Dermatobia, or naked, like those of the young 
Hypoderma, or with horny stigmatal plates, like those of Cephenomyia. The 
remarkable parasitic method of life in mammals can probably be looked upon as 
peculiar to the (stride. I leave it, therefore, to a future observer to establish a 
character for the estrid lary whereby they may be distinguished from all other 
muscid larve, and limit myself here to the description of the larve according to 
genera and species. 
The estrid larve belong to the great division of those dipterous maggots which 
have been called headless; since they are segmented throughout and the usual regions 
of the insect body are not separated. Only a cephalic and an anai end, therefore, 
can be distinguished on the annulate body of such larve. In general the following 
common characters and peculiarities of the cestrid larve can be specified. 
(1) The body of all cestrid larve is really composed of twelve rings. The first 
two are, however, not always distinctly separated, so that I take them together in 
the description, and designate them both by the name of cephalic ring, on which in 
many cases an anterior and posterior section is clearly to be distinguished. On that 
account I assume only eleven segments, as earlier authors havedone. Only the new- 
born larve of Gastrophilus make an exception to this number; they, if Joly’s state- 
ment is correct, possessing thirteen segments. 
(2) Two anterior, external breathing organs are always to be distinguished on the 
larv, between the first and second segments of the body, and two posterior, exter- 
nal breathing organs on the last ring. The former are very small and appear either 
as points, knobs, or fissures, or the anterior ends of the trachew are hidden entirely 
in a cylindrical invagination of the skin (Gastrophilus). The posterior breathing 
organs are either breathing tubes which are protrusile and retractile (new-born Gas- 
trophilus larve [p. 36] and Cephenomyia larvze), or large stigmatal plates which are 
constructed according to two kinds of types. One of these types is represented in 
Gastrophilus and Dermatobia, the other in the rest of the genera. The stigmatal 
plates are more or less protected by lip-like organs on the last ring or by withdrawal 
into the preceding ring, and are in this way cleaned from substances which adhere 
to them. 
Ihave described in detail under that genus the structure of the posterior stigmatal 
plates in Gastrophilus. The majority of the genera possess, however, two stigmatal 
plates in a real sense, consisting of corneous chitinous substance on the last ring. 
Each ring is usually crescent-shaped or reniform, in younger larve even quite cir- 
cular, and appears when magnified either as latticed with coarse meshes, finely 
porous or almost smooth, sometimes radially furrowed. On the inner border of each 
plate is in all larve in the third and in many in the second stage a thinner, mem- 
branous or knob-like place superposed or embedded, sometimes inclosed in the plate 
itself. The attachment of the trachea corresponds to this place on the inside. Since 
it usually has the appearance of an opening, and aiso has been taken for such, I call 
it the false stigmatal opening. It has not yet been ascertained without doubt that 
breathing goes on in such stigmatal plates, but it probably takes place through 
pores of the plate. It seems tome as if the plates were penetrable especially at the 
circumference of the attachment of the trachee. 
(3) The new-born larve all possess external mouth parts; in the later stages 
larve with oral hooks and those without them are to be distinguished. An internal 
pharyngeal framework of various development always occurs; this incloses the 
membranous gullet and by its muscular structure 1s of essential service in the suck- 
ing of the larva. If oral hooks are present, they are connected with this by a joint. 
