276 Scientific Proceedings, Royal Dublin Society, 



processes (figs. 22, 24, 26, 28, P. 9), which doubtless correspond with the 

 similarly placed structures in the female, and with the valves of male 

 Lepidoptera assigned by Peytoureau ('95) to the ninth segment. In 

 his figure of the male genitalia of Eristalis, Berlese ('09, p. 327, fig. 395) 

 shows two pairs of processes — " acrocerci " and " mesostyli " ; probably the 

 structures now under discussion correspond with the latter. It seems to us 

 that Berlese is mistaken in reckoning the genital segment as the tenth. In 

 H. bovis these processes are evenly rounded at their edges, and project 

 inwardly in blunt, spiny tips, which are visible ventrally (fig. 24), but not 

 dorsally (fig. 25). The corresponding parts in S. lineatum have a very different 

 aspect, projecting backwards as more prominent lobes, of which tlie strong 

 chitin is arranged in two bands forming a narrow arch, with membranous 

 cuticle between (fig. 26, P. 9). The tips of these processes are rough, beset 

 with a thick hairy covering, and being more slender and less incurved than 

 the corresponding structures in H. bovis, are visible dorsally (fig. 29) as well 

 as ventrally (fig. 28). The ventral edge of the process in H. bovis is continued 

 forwards on each side into a slender, delicate ridge (figs. 22, 24, p.), bounding 

 the membranous cuticle which touches the thickened hinder edge of the 

 pre-genital sternum (St. 8), directed dorsalwards and inwards. Also from the 

 ventral edge of the ninth tergum a broad membranous epipleuron (figs. 22, 

 24, 26, 28, ep.) extends forwards and joins the lateral edge of the pre-genital 

 sternum. In H. lineatum this epipleuron is sub-triangular as seen laterally, 

 while in H. bovis it is erescentic. 



The tenth tergum in both species tapers at the hinder end, which is 

 prolonged into a ventrally directed point. This corresponds to the " uncus " 

 of male Lepidoptera, recognized by Peytoureau ('95, p. 52) as the tenth 

 tergum. In H. bovis its edges are rounded, and there is an extensive central 

 white membranous area (fig. 25, x) ; in H. lineatum it is more nearly triangular 

 in form ; its front edge produced into a median point and its hinder apex 

 prominent (figs. 29, x, 26 A). The appearance of the tail-region is thus very 

 different in the two species (compare figs. 22 and 26, 25 and 29), but there is 

 no marked difference in size, such as can be observed in the ovipositors, the 

 male's terminal segments in H. lineatum being as large as in S. bovis. 



The most extensive part of the ventral exoskeleton in this region is the 

 pregenital sternum (figs. 22, 24, 26, 28, 30, St. 8), which is narrowly rounded 

 in front, broad behind, and bent dorsalwards on either side. As already 

 mentioned, delicate curved processes from its hinder edge meet similar out- 

 growths from the ninth tergum. This sternal area is called by Lowne tlie 

 "progenital sternum" ; by Briiel the " Gabelplatte " ; and by Gordon Hewitt 

 " the body of the penis." Both Briiel and Lowne believe that it belongs to 



