76 INSECTS AFFECTING DOMESTIC ANIMALS. 
Of the organs in which (stride occur, the skin, or really the subcuticular cellu- 
lar tissue, is that which is the most strongly attacked; the larvee of four genera— 
Hypoderma, (Estromyia, Dermatobia, Cuterebra—live init. The nasal and frontal 
cavity are inhabited by the genera Cephalomyia and (éstrus, the nasal and cesoph- 
ageal cavity by the genus Cephenomyia, the intestinal canal by the genus Gastro- 
philus. The transformations cf the other genera of {stride are unknown. 
It is interesting, further, that many genera occur only as parasites of certain fami- 
lies of mammals, while others have a somewhat wider or very wide range of distri- 
bution, and so have for hosts the different mammals, yet not quite without choice, 
and often even seek man for their breeding places. 
Thus, until now, the larvie of Cephenomyia have only been found in the throats of 
cervina, those of the genera Cephalomyia and Céstrus only in tylopoda and cavicornia, 
those of the genus Gastrophilus in solidungula and multungula (Rhinoceros), but 
Hypoderma, on the other hand, in cavicornia (Bos, Capra, Antilope), cervina (Cervus, 
Moschus), and equida, Cuterebra larvze in Rodentia and Marsupialia, and finally those 
of Dermatobia in dogs, oxen, horses, and even upon man. 
(p.40) Another picture is formed if the perfect insects are divided according to a 
peculiar character into those with pectinate antennal bristles (Cuterebra, Derma- 
tobia), and those with naked antennal bristles (Hypoderma, Gastrophilus, Cephe- 
nomyia, Cephalomyia), since the larvie of the former are parasitic in ungulate 
animals as well as especially in Rodentia and Marsupialia, but those of the latter 
only in Ungulata. This hitherto so convenient and practical division likewise can 
not be relied upon for an inference, since (strus leporinus belongs to the group of 
(Estrid:e with naked bristle, but its larva lives upon a rodent. It is seen that such 
divisions are only artificial and serve for orientation, but that nevertheless nature 
can not be forced into them. Such divisions are therefore only temporary, and only 
too often become untrue so soon as new discoveries are published. It is therefore 
best to treat of the larvee according to their genera, and to limit these as natually 
as possible, since it has thus far been found constantly in this family that the larve 
of one genus all have a like life history, and conversely the generic characters of the 
imagoes can scarcely lead us astray if we wish to draw an inference as to the life 
history of a larva perhaps not yet investigated. In the case of a new genus, how- 
ever, we can infer its life history with very little certainty. Experience alone 
teaches this. 
The flies are seldom observed except in open sunny places and secrete 
themselves mostly in low herbage, grass, along roadsides, and other 
situations where they may gain ready access to their victims. Most or 
all of them live in this stage strictly without food, the mouth parts, 
except in a few, being very rudimentary or entirely wanting. All are 
confined in their attacks to vertebrates, and all, so far as positively 
known, to mammals. 
The species are quite numerous, about sixty being known in the adult 
form, but only the more common ones have been thoroughly studied, and 
in our detailed discussion of the species we will give particular atten- 
tion only to those affecting the common domestic animals. 
THE HORSE BOT-FLY. 
(Gastrophilus equi Fab.) 
Bots in horses have been a familiar form of parasite to farmers, 
stockmen, and veterinarians for we know not how long. Whether they 
were familiar to the ancients has been a matter of discussion among 
