94 [April, 



'■ The Amurican Ox VVaiblc, in every ease so far observed, is the larva of 

 Hypoderma lineata* This species has eoiiie to be known, especially through the 

 south and south-west, as the Heel Fly, on account of the habit which the female 

 has of frequenting the legs of animals for purposes of oviposition. While the eggs 

 are laid on other parts of the body tiiat may be reached by the tongue, the species 

 shows quite a strong tendency to select the flanks and legs around the heels, and 

 the habit, almost everywhere observed, that cattle have of seeking to ]irotect their 

 legs by running into water daring the bot-fly season finds its explanation in these 

 facts. The eggs are attached firmly, by a strong cleft, in rows of from five to ten 

 or more, to the hairs. (For figures of the eggs, see op. ciL, p. 307, fig. 41). 



" When the cattle lick themselves, the young larva) are taken into the mouth, 

 as, under pressure and moisture, the egg readily splits at its anterior end, and 

 releases the young larva, which is already well developed when the egg is laid. 

 Doubtless quite frequently the eggs with the contained larvae are taken with the 

 hair in this licking, but in either event the larva in leaving the egg is armed with 

 many minute spines, which permit it to adhere to and to penetrate the walls of the 

 oesophagus. Here it soon moults and takes on the second or smooth stage, which 

 for eight or nine months wanders slowly in the tissues of its host. The slow move- 

 ment and the little nourishment taken reduce the inflammation and irritation to a 

 minimum ; in fact, the most remarkable thing in the life-history of this larva is the 

 long period of latency, and the slight development that takes place during the 

 summer and autumn months. During the late winter the larva reaches a point 

 beneath the skin in the region of the back, and penetrates the skin, anal end first, as 

 Dr. Curtice believes, and as seems most probable. Here it moults a second time, 

 and re-assumes its spinous character, producing more or less inflammation and de- 

 veloping rapidly, with its enlarged spiracles fitted for more perfect breathing. The 

 third moult soon follows, and we get the more strongly spined grub, with its still 

 larger spii'acles, which lives in the swellings or sacs so well known to stockmen. It 

 finally woi'ks its way out, drops to the ground, which it enters, and where it 

 contracts, hardens, and darkens in colour. In a few weeks afterward the perfect fly 

 issues. 



" That such is the normal and invariable life-history of Hypoderma lineata I 

 think there can no longer be a doubt, and the burden of proof of any departure 

 from it will rest hereafter with those who contend otherwise." 



The early stages of the larva of Hypoderma hovis have recently 



beeu studied by Koorevaar in Amsterdam (" J'ijdschrift der Neder- 



landsche Dierkundige Vereeniging," 2de serie, deel v (1S9S), pp. 



29 — 34: — c/! translation by the present writer in Ann. Mag. Nat. 



Hist., ser. 7, vol. 4 (1899), pp. 69 — 78), with a view to discovering 



whether the Hypoderma larva?, which are frequently met with within 



the spinal canal of cattle, lying in the fat surrounding the spinal 



cord, as well as in the wall of the oesophagus, are really the same as 



those often found iu the same animal in warbles beneath the skin. 



From the results of his experiments with living Hypoderma larvae 



* In connection with this statonient it is worthy of note that, from evidence afforded by the 

 series of specimens in the British Museum (Natural History), H. lineatum is far more common 

 than U. bovis iu England also. 



