490 SYNOPTIC COLLECTION. 



is straight ; that is, the head, thorax, and abdomen are in 

 a horizontal line, while the body of Culex is hump- 

 backed. 



Among the most carnivorous Diptera, both in the lar- 

 val and adult stages, is the robber-fly, Asilus sericeus Say 

 (No. 1255). It is well adapted for the life which it leads, 

 by having a robust body, bristling with stiff hairs, a 

 strong, black proboscis able to inflict severe wounds, legs 

 armed with spines and fitted for running, seizing prey, 

 climbing, and digging, and wings with muscles capable of 

 rapid flight. 



Many of the specializations of the Diptera are well 

 shown in the type form, Tabanus. The larva (PL 1256, 

 fig. i, Tabanus atratus Fabr.) tapers at both ends and in 

 this way differs from the larvae of the Tipulidae. It is a 

 footless animal with a head provided with curved dark 

 brown mandibles. 



The pupae (fig. 2, Tabanus lineola Fabr.) are free and 

 may be distinguished by the large, ear-shaped spiracles 

 on the thorax. In the Orthorhapha the winged insect 

 emerges through a slit on the back of the pupa. The 

 short, compact body of the adult (No. 1257; PL 1256, 

 fig. 3 ; No. 1258, a larger species of Tabanus) exhibits 

 extreme concentration of parts, while at the same time 

 the three regions are sharply differentiated from one 

 another. 



The broad head with its great compound eyes is on a 

 pivot-like neck. The thorax is complex in structure, 

 differing from the more generalized thorax of the Tip- 

 ulidae. The reduced collar-like prothorax (PL 1256, fig. 

 4,/) is firmly soldered to the large mesothorax (fig. 4, 

 ms). The metathorax (fig. 4, mt) is only partly seen 

 from above, the basal portion of the abdomen having 

 crowded forward and covered up its posterior, dark- 

 colored bulbous portion or scutellum (fig. 4, sc r "). This 

 part is still better seen in fig. 5. which is a drawing of 

 the head and thorax seen from the side. This peculiar 



