327 
C. Warburton 
crawls away in search of a retreat—preferably a hole in the ground. Here its 
integument quickly hardens to form a puparium, its colour deepening to a 
very dark brown or black hue. The pu^al period depends on the temperature, 
but averages about five weeks. The fly then bursts open a triangular operculum 
on the antero-dorsal portion of the operculum, and the metamorphosis is 
achieved. 
II. The Evidence Discussed. 
The Flies. 
It is not proposed here to include diagnoses of insects which have long been 
perfectly well known, though at a later stage it may be useful to give directions 
for distinguishing the imagos and the different larval instars of the two species. 
The present account is largely historical. 
The poverty of entomological collections in specimens of Hypoderma 
and the difficulty which the earlier investigators experienced in breeding 
out imagos or in capturing examples in the open are exceedingly striking. 
It was some years before Yallisnieri succeeded in breeding out the single 
imperfect specimen which he described in 1710. Reaumur was more fortunate. 
Finding that the cattle in the open country near Paris were free from warbles 
but that many in the wooded district near Brie l’Abbaye were badly infested, 
he obtained his material from that region. Unable to be absent from Paris at 
the time the larvae left the cattle, he persuaded the Mother Superior to lend 
him two infested heifers, and had them so closely watched that he was enabled 
to observe the emergence of several larvae, from some of which he obtained 
excellent specimens of the fly. His most valuable observations were published 
in 1738. In 1776 de Geer named a fly which was captured “in the country,” 
and which he considered identical with Reaumur’s specimens, Oestrus hovis, 
and in 1825 Latreille founded the genus Hypoderma. 
Bracy Clark, who published his first paper on the subject in 1797 and 
whose famous ‘ Essay ” was issued in 1815, began his investigations in ignorance 
of the work of Vallisnieri and Reaumur, being misled by Linnaeus, whom he 
supposed to be acquainted with their writings. Linnaeus, however, had entirely 
confused the ox bot-fly with that of the horse, and his Oestrus hovis is nothing 
but Gastrophilus intestinalis (equi), and it was not until much of Clark’s 
research was completed that that writer became aware of the discoveries of 
his predecessors. 
Clark first introduced the method of “sleeving,” or fixing muslin bags over 
the warble tumours so as to capture without injury the larvae as they emerged, 
and by this means he obtained several specimens of the fly. Joly (1846) based 
his anatomical studies of the fly on three specimens only, and the material 
of Brauer (1863) was hardly more plentiful. 
Up to 1890 all the observations on ox-warbles were attributed to the 
species H. hovis. It is necessary to bear in mind, that previous to that date 
the insect concerned in many of the European cases, and probably in all the 
