Carpenter & Hewitt — Genitalia and Larva of the Warhle-fly. 281 



formidable mouth-hooks and spiny armature of the tiny maggot that emerges 

 from the Warble-fly's egg. 



This first-stage maggot (Plate XXVI, figs. 31, 32) is '8 mm. in length. In 

 dorsal or ventral view (fig. 32) both the front and hind ends are rounded, 

 but in side view (fig. 31) the head-end is much narrower than the tail, 

 recalling the form of a typical muscoid maggot, and suggesting that this 

 earliest instar of tlie Hypoderma larva is far less specialized than those later 

 forms which are adapted for parasitic life within the body of the ox. The 

 segmentation of the body corresponds to the arrangement found in muscoid 

 larvae ; there are the usual twelve obvious segments. According to Lowne 

 and Gordon Hewitt ('08, PI. 30, fig. 5) the apparent second segment, which 

 usually has the paired anterior spiracles at its front edge, is really the 

 fourth, and the tail-segment on which the large posterior spiracles open is the 

 thirteenth. We believe that this hinder spiracular segment is the ninth 

 abdominal; behind this the minute tenth (anal) segment (fig. 31, A) can be 

 seen ventrally. But this little maggot yields no guidance as to tlie disputed 

 questions of the segmentation of the anterior region, unless it be in the 

 anomalous position of the front spiracles. 



The anterior spiracles are usually not recognizable in the first instar of a 

 muscoid larva ; later they appear at the front edge of the apparent second 

 segment. But in this first-stage lax'va of Hy2)oderma bovis we find a pair of 

 spiracles at the far front end dorsal to the mouth (figs. 31, 32, 35, A. Sp., 36), 

 apparently a segment in advance of their normal position. Eiley saw these 

 structures in the unhatched larva of H. limatum, and recognized their spiracular 

 nature, which is now questioned by Glaser, who calls them " filhlerartige 

 Vorstulpungen," and says ('13, p. 31) that lie can trace no tracheal tubes in 

 connection with them. We have, however, succeeded in finding distinct 

 tracheae (fig, 35, Tr., 36) which have close to the opening a thickened 

 chitinous lining. In our specimens the spiracles do not project in front of 

 the head ; the cuticle around is thickened in the form of radiating ridges, 

 and it is likely that under certain conditions they might be protruded. 



The mouth-armature has been described and roughly figured by Grlaser 

 ('13, pp. 31-2, fig. B). We find that in S. bovis the mout/i-hootcs (Plato XXVI, 

 figs. 31, 32, 33, 35, H) articulate directly with tlie pliaryngeat sclerites (figs. 33, 

 35, Ph.), the paired hypostomal sclerites that intervene in most half-grown or 

 full-grown muscoid larvse (see Banks, '12, pp. 14-15; Lowne, '90, pp. 44-5, 

 fig. 9) not being present ; according to Lowne these sclerites are not 

 recognizable in the Blow-fly maggot till after the second moult, so that their 

 absence in the young Warble-maggot might have been expected. The 

 pharyngeal sclerites are of the usual form, the ventral processes being somewhat 



