316 MEDICAL ENTOMOLOGY 



inadequate, for while the species of a genus may agree in their parasitic 

 life histories, the larvae of different genera may have the same 

 habits. He instances the habits of the larvae of Hypoderma, Cnterebra, 

 Dermatobia and Cephenoinyia, and points out that there is far more 

 difference between the mature insects of one and two, than between two 

 and three. The larvae of Cephenoinyia live, as a rule, in the oesophagus, 

 the Oestrus larvae in the frontal and nasal cavities, the Gastrophilns 

 larvae in the intestinal tract, and those of Hypoderma in the subcutan- 

 eous cellular tissues. 



The adult flies have been grouped according to the structure of the 

 antennal bristles, into those in which they are pectinate (Cnterebra 

 and Dermatobia), and those in which the bristles are naked (Hypoderma, 

 Gastrophilns, Cephenoinyia, Cephaloinyia) ; the larvae of the former are 

 found in the bodies of Rodents and Marsupials, and in Ungulates ; 

 those of the latter only in Ungulates. These groups are, however, un- 

 natural, for the larvae of Oestrus leporinus, which has naked bristles, is 

 parasitic in a rodent, as its name implies. Brauer considers it best to 

 classify the larvae according to their genera, for those of each genus have 

 a similar life history. The generic characters of the imago always 

 afford a reliable clue to the probable life history of an unknown larva ; 

 in the case of new genera experience is the best guide in predicting the 

 probable life history of the larva. 



WILLISTON'S KEY TO THE GENERA OF THE OESTRIDAE. 

 Imagines. 



1. Mouth parts very small, vestigial ; arista bare ...... 2 



Proboscis geniculate, inserted in a deep slit ; female without 



extricate ovipositor ; first posterior cell narrowed or closed ; 

 arista bare or plumose ; facial grooves approximated below, 

 enclosing a narrow median groove or depressed surface ; 

 squamae large 6 



2. The fourth longitudinal vein runs straight toward the border 



of the wing, i.e., the apical cross-vein is obsolete, and the 

 first posterior cell is narrowed ; squamae small ; female ovi- 

 positor elongate ; larvae in stomach and intestinal canal . Gastrophilus. 

 The fourth vein turns forward to form the apical cross-vein, 



closing or narrowing the first posterior cell ... ... 3 



3. Facial grooves approximated below, leaving a narrow median 



groove or depression ........ 4 



Facial grooves remote, enclosing between them a broad, gent- 

 ly arcuate, shield-shaped surface ; squamae large ; female 

 with elongate ovipositor ; larvae hypodermatic ... ... 5 



4. First posterior cell closed and petiolate ; body nearly bare . Oestrus. 

 First posterior cell narrowly open ; body pilose . . . Cephenomyia. 



