Carpenter & Hewitt — Genitalia and Larva of the Warhle-fly, 283 



from the Horse's stomach, in which (see Text figure) the mouth-liooks are 

 very strong and divergently directed, while each parastomal sclerite is 

 separately prolonged into a sharp forwardly directed spine. 



We have had no opportunity of studying first-stage larvae of Hypoderma 

 lineatiim. Glaser states ('13, p. 32) that the mouth-armature is altogether more 

 strongly built in that species than in H. bovis. 



As already remarked, the body-segments of our little larva are remarkable 

 for their strong spiny armature. There are seven or eight irregularly 

 arranged rows of spines around most of the segments, two or three series 

 of strong spines being found close to the front edge of each segment, those 

 behind being feebler, and the posterior margin of each segment showing a 

 strip free from spines. Glaser states ('13, p. 31, PL iv) that the S. lineatum 

 larva has stronger spines than that of H. bovis, and that the dorsal 

 surface of the larva in both species has stronger spines than the ventral. 

 In tliis latter opinion he is in error, having mistaken the ventral surface for 

 the dorsal. When the larva is examined in side view (PL XXVI, figs. 31, 35), 

 no doubt as to the orientation is possible, and the strong spines are clearly 

 seen to be ventral in position. This is the arrangement, as is well known, 

 in muscoid maggots generally, as spines, being of service in locomotion, 

 are naturally best developed on the surface whereon the larva crawls. It is 

 further of interest to find that in the young larva of Hypoderma hods, the 

 dorsal aspect of the two hindmost abdominal segments (fig. 31) is almost 

 devoid of spines, for the unarmed condition of these terga in the fourth- 

 stage maggot has long been recognized as a specific character by which 

 H. bovis may be distinguished from H. lineatum in the larval stage. (See 

 Riley, '92, p. 311.) We may add that the result of rearing flies from maggots 

 which emerged from the backs of cattle, and were determined by us before 

 pupation, has in all eases confirmed the reliability of the larval characters. 



The terminal or hind spiracular segment of the young larva is of especial 

 interest. At its front edge on the ventral surface are four or five rows of 

 very strong spines, which, like all the spines on the preceding segments, point 

 backwards (figs. 31, 32). Behind these are about a dozen weaker spines 

 arranged in a transverse row, and directed forwards. Behind these again, 

 the broad posterior aspect of the larva is covered with numerous very strong 

 curved hook -like spines, most of which point dorsalwards (see figs. 31, 34). 

 In the midst of these are situated the posterior spiracles (figs. 31, 32, 34, P. Sp.) 

 circular openings, close together near the median line, each surrounded by a 

 thickened chitinous margin, and guarded by two or three extra long spines. 

 From the condition of some of our specimens, we infer that tlie spiracular 

 area can be invaginated so that the openings may be protected by an infolding 



SCIENT. PBGC. R.D.S., VOL. XIV., NO. XIX. 2 Y 



