July— September 1SS5.J 



PSJ'CIIE. 



309 



full-grown larvae, but scientificallv un- 

 natural and incorrect, since in the first 

 place this peculiarity of the full-grown 

 larvae corresponds to no similar degree 

 of relationship of the perfect insects, 

 and in tiie second place it is only tem- 

 porary, [p. 39] since all oestrid larvae 

 possess oral hooks when they are quite 

 young. Such a division also as Clark 

 attempted to make, into cavico/ae, ciiti- 

 colae^ and gasiricolae., is inadequate, 

 for while the species of a genus do in- 

 deed always agree in life-history so far 

 as their occurrence as parasites in a de- 

 terminate organ is concerned, neverthe- 

 less the larvae of very different genera 

 may also share this same manner of 

 life with others ; for instance, Hyfo- 

 derma, Cuterebra, Derfnatobia, among 

 which there is far more diflerence be- 

 tween I anil 2 than between Cutcrebra 

 and Ccphenomyia, if the imagines are 

 considered. Such a division is there- 

 fore likewise not a natural one, since it 

 disturbs the natural relations of affinity. 

 Two elements must be considered, in 

 order to bring about an approximately 

 natural division : in the first place the 

 organization of the larvae, 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 oi oestri- 

 dae of one genus having been found 

 parasitic in different systems of organs. 

 Thus the Cephenotnyia larvae belong 

 to the oesophagus, the Cephalomyia 

 and Oestrus larvae to the nasal and 

 frontal cavity, those of Gastrophihis 



to the intestinal tract, and those of Hv- 

 podernia to the subcuticular cellular 

 tissue. 



Althougji it is stated that the larva 

 of GastropJiilus has been found in the 

 oesophagus, this is one of the excep- 

 tional cases which are not authenticated. 

 Of course only the full-grown larva is 

 meant here, since young larvae may 

 always be found in other places during 

 the immigrations. So for instance the 

 young Oestrus and Ccphenoniyia lar- 

 vae both immigrate in like manner 

 tlirough 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 oesopha- 

 geal cavity. 



Of the organs in which ocstridae 

 occur, the skin, or really the subcu- 

 ticular cellular tissue, is that which is 

 the most strongly attacked; the laivae 

 of four genera : Hvpoderma, Ocstro- 

 myia, Dermatobia, Cuterehra, live in 

 it. The nasal and frontal cavity are 

 inhabited by the genera Cephalomyia 

 and Oestrus, the nasal and oesophageal 

 cavity by the genus Cepheiiomyia, the 

 intestinal canal by the genus Gastro- 

 pJiilus. The transformations of the 

 other genera oi ocstridae are unknown. 



It is interesting farther that many 

 genera occur only as parasites of certain 

 families of mammals, while others have 

 a somewhat w'ider or very wide range 

 of distribution, and so have for hosts 

 the different mammals, yet not quite 

 without choice, and often even seek 

 men for their breeding places. 



Thus until now the larvae of Ccphe- 



