52 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



axillary, but is sometimes carried directly by the axillary membrane, 

 while in a genus of beetles (Cyllene) it is attached to a special process 

 of the postnotum. In the honey bee the coxo-axillary muscle is 

 inserted upon a sclerite which appears to be an epimeral parapterum. 



Legs. — In adults the legs are attached to the ventrolateral regions 

 of each thoracic segment, typically between the pleurum and the 

 sternum, and behind the middle of the segment. The basal segment 

 or coxa (figs. 5 and 7, Cx) is articulated above to the pleural coxal 

 process (CxP) at the lower end of the pleural suture (PS), and below 

 to the lower end of the trochantin (Tn). If the trochantin is absent, 

 as it generally is in the higher orders, the coxa either has no ventral 

 articulation or it articulates with a knob of the sternum. Wlien the 

 trochantin appears to be absent it might, of course, simply be fused 

 with the sternum, in which case the apparent sternal coxal process 

 may be really the trochantin al condyle. 



The coxa is a double structure in the mesothorax and metathorax 

 of Neuroptera, Mecoptera, Trichoptera, and Lepidoptera. Some 

 writers have argued that this is evidence of each segment's being 

 composed of two fused primitive segments. The writer, however, 

 has elsewhere (1909) shown reason for believing that the posterior 

 subdivision of the coxa in such cases is simply the lower part of the 

 epimerum detached from the latter and fused upon the true coxa. 

 This is indicated by a study of larval and pupal forms, and conse- 

 quently, if so, the double nature of the coxae in these orders is a 

 purely secondary character and can have no morphological signifi- 

 cance, unless, indeed, it be assumed that the simple larval coxae are 

 specialized and that in the pupal and adult stages the legs revert to 

 a more primitive ancestral character. 



The next joint of the leg, the trochanter (fig. 5, Tr), is apparently 

 double in some of the Hymenoptera, but in such cases it looks more 

 reasonable to regard the "second troclianter^' as a basal subdivision of 

 the third joint ov femur (F). 



The characters of the tibia {Th) and tarsus {Tar) are too familiar to 

 require any special discussion here. The under surface of each tarsal 

 joint is sometimes provided with a pair of small cushion-like pads, 

 which were named the pulvilli (Pv) by Kirby and Spence (1826). 

 Most authors, however, would understand by "the pulvilli" only 

 those pads of the terminal segment occurring at the bases of the claws. 

 The terminal segment frequently bears also a median fleshy append- 

 age between the claws, which is known as the emjjodium (Emp). 

 All of these soft appendages of the tarsus enable the insect to adhere 

 to smooth surfaces by a sticky liquid excreted upon them. The 

 Hymenoptera possess only the median appendage of the terminal 

 segment. 



