CUTANEOUS OESTRIM: 595 



CUTANEOUS OESTRID^:. 



The eggs are deposited on the surface of the body ; the larvae burrow in the 

 skin, which they reach after somewhat long peregrination. 



Genus. Hypoderma, Latreille. 



Hypoderma bovis, de Geer. 



The cattle fly or warble fly, which swarms during the hot season, settles on the 

 head or on the hair of grazing cattle : through the young being licked off they gain 

 access to the mouth and are swallowed. 1 The larvae appear first in the commencing 

 portion of the stomach, to escape, as some state, into the preceding sections of the 

 alimentary canal ; at any rate, they are found from July onward regularly in the 

 submucous tissue of the pharynx, in which they travel about for several months 

 (up to November, and in isolated cases up to February) ; they then penetrate the 

 muscularis and migrate by way of the subserosa along the mediastinum, the crura 

 of the diaphragm, the renal capsules, and the intermuscular connective tissue of the 

 psoas muscle in the direction of the spinal canal, into which they penetrate by way 

 of the muscles and nerves, through the intervertebral foramina. Here they stay for 

 about two to three months, then they leave the spinal canal again through the 

 vertebral foramina and make their way (from January to March) through the inter- 

 muscular connective tissue of the muscles of the back to the skin of the back, where 

 sooner or later (from January to June) they arrive and enter a resting stage, which 

 commences with penetration of the skin and terminates with outward migration 

 from the boils due to the wound set up by the maggot. At the commencement 

 of this period the larvae cast their skin, and their form, hitherto cylindrical, becomes 

 oval. After about a month, a second moulting of the skin takes place the third 

 larval stage, which lasts about two and a half months (up to June). The approaching 

 end of the same is indicated by a change of colour on the part of the larva from the 

 hitherto yellowish-white to brown and finally to blackish-brown. When they have 

 become mature the larvae leave the warbles, drop on to the ground and pass into 

 the pupal stage in the superficial layers of the soil within twelve to thirty-six hours. 

 After about a month the flies emerge. Irregularities with regard to the time and 

 direction of the migrations of the larvae take place (Jost, H., in Zeitschr. f. iviss. 

 ZooL, 1907, xxxvi, p. 644). 



In a number of cases the larva of the cattle fly has been observed 

 in the human integument, usually in the winter months, that is, 

 during the migration period ; consequently, it is not surprising that 

 the larvae before they enter on the resting stage and produce a warble 

 undergo migrations. But that this takes place subcutaneously 

 which does not appear to be so in the case of cattle is perhaps 

 explained by the fact that in man, on account of the short space that 

 has to be traversed, the larvae are not sufficiently developed to enter 

 on the resting stage simultaneously upon having obtained access 

 to the integument. Whether the Oestrid larvae in Bulgaria that 

 similarly migrate beneath the skin in man belong to the cattle fly 

 or to another species, or even another genus, has not yet been 



1 [This is not the case, for Carpenter has shown that muzzled calves become infected 

 ("Mem. First Int. Cong. Ent.," pp. 289-293). Jost (Zeiischr. f. wiss. ZooL, 1907, xxxvi, 

 pp. 644-715) thinks that the ova, not young larva;, are ingested (vide note in Supplement. 

 F. V. T.J- 



