Carpenter & Hewitt — Genitalia and Larva of the Warble-fly. 271 



slender. There are two spermathecse on the right, with ducts markedly longer 

 than that of the single capsule on the left. This arrangement of two sperma- 

 thecse on the right, and one on tlie left, seems usual among Diptera ; we 

 suspect that Gordon Hewitt ('07, p. 430) may be mistaken in describing in 

 the House-fly two on the left and one on the right. In Hypoderma we find 

 that the ducts of the right-hand couple are closely connected together 

 throughout the terminal thickened part of their course ; the left-hand duct, 

 except in its furthest distal region, is free from the other two (fig. 4, d.). 



On the wall of the spermatheca may be seen transverse striations and a 

 number of dark red spots. When examined with high magnification, the 

 strisB are seen to be thickened^ridges of the chitinous coat, and the spots to 

 be minute curved hooks (fig. 4 A), which are on the outside of the chitin, 

 and in contact with the thin outer fibrous sheath of the spermatheca. In a 

 fully extended ovipositor of H. lineatum the spermathecse are visible through 

 the thin cuticle just in front of the sixth abdominal segment (Plate XXIII, 

 fig. 14, sp.). 



3. The Ovipositor. 



Sufficient material has been at our disposal for a comparative study 

 of the ovipositor in the two species of Hypoderma. It is well known that 

 the ovipositor of a dipterous insect consists of the hinder abdominal segments, 

 which are modified into cylindrical or sub-cylindrical tubes, their sclerites 

 joined by long tubular tracts of intersegmental cuticle, so that the segments 

 can be successively telescoped into one another from behind forwards, the 

 eighth and ninth into the seventh, the seventh into the sixth, and the 

 whole then telescoped into the fifth segment, when the ovipositor is retracted. 

 In the most highly specialized Diptera, such as the House-fly (Musca) (see 

 Gordon Hewitt, '07), the sclerites of these ovipositor segments are reduced 

 to narrow chitinous rods. It is of interest to note that in Hypoderma the 

 specialization is less extreme ; in both species most of the sclerites are plates 

 long and narrow indeed, but not of the excessively attenuated form to be 

 seen in the corresponding parts of Musca. On the other hand, the condition 

 in Hypoderma is more specialized than in Eristalis, whose sixth and seventh 

 abdominal sclerites are comparatively sliort and broad according to the 

 description and figures of Lacaze-Duthiers ('63, pp. 80-1, pi. v, fig. 6). A 

 short account of the ovipositor of Hypoderma is given in the recent paper 

 of Glaser ('13); his illustrations, however, are mostly photographic, and on 

 too small a scale to bring out the more minute features. 



At least four abdominal segments — the sixtli, seventh, eighth, and ninth — 

 help to build up the ovipositor (PI. XXII, figs. 5, 6, and PI. XXIII, figs. 13, 



