Caupkntkr and Pollard — Lateral Spiracles in ilypoderma Larva. 75 



present as well as an anterior pair of functionless spiracles just behind the 

 mouth ; these latter, which were recognized and figured by Joly ('46, pi. viii, 

 fig. 2, o) in the ripe maggot of Hypoderma bovis, and by Brauer ('68, Tab. viii, 

 fig. 4) in the final-stage larva of Oedemagena tarandi, seem to correspond with 

 the prothoracic, fan-like spiracles of the typical inuscoid maggots. 



The lateral spiracles in the Hypoderma larva were revealed to us through 

 the observation, on dissection, of the white and thread-like solidified air-tubes 

 connecting branches from the longitudinal tracheal trunks with the body-wall, 

 outside the cuticle of which, when thus directed, we had little difficulty in 

 recognizing the tiny spiracular depressions, So far we have not succeeded in 

 finding these lateral spiracles in the earlier instars of Hypoderma, nor in any 

 muscoid maggots that we have had the opportunity of examining, nor in 

 the familiar " leather-jacket " grub of the Crane-fly (Tipula). But as we have 

 made a fairly full study of the structures in the ripe (fourth-stage) Hypoderma 

 larva, we offer our results as some contribution to a fascinating morphological 

 question, hoping that we may be able to supplement our observations at some 

 future date. Before proceeding to the detailed account of the newly discovered 

 spiracles and their relation to the tracheal system, some references to the 

 segmentation of the Warble-maggot and the structure of its cuticle are 

 necessary. 



The Segmentation of the Hypoderma Larva. 



Students of the maggots of the most highly organized Diptera have all 

 recognized the difficulty of interpreting the body-segmentation of these larvae 

 — at once so specialized and so degraded. The forward end shows, as is well 

 known, no definite head, but two or three segments seem to be present in 

 front of that which bears the small anterior spiracles. This segment, according 

 to Lovvne ('92, pp. 34-5, fig. 10), is the fourth ; according to Hewitt ('08, p. 511, 

 pi. 30, fig. 5), the third post-oral somite, so that the " tail-segment " which 

 bears the posterior spiracles is the fourteenth according to Lowiie's or the 

 thirteenth according to Hewitt's reckoning. Neither of these authors suggests 

 what correspondence any of these segments may have with those of a gene- 

 ralized insect, but Hewitt's enumeration may perhaps imply that, the head 

 being degenerate, the segment of the anterior spiracles may be the meta- 

 thorax. Now it seems to us that consideration of the segment of the posterior 

 spiracles may yield more certain guidance, and that as in insects generally 

 the hindmost spiracular segment is the eighth abdominal, this is the correct 

 identification of the " tail- segment" of a muscoid maggot. The segment of 

 the anterior spiracle will thus be reckoned — in conformity with the opinions 



