30 ILLINOIS BIOLOGICAL MONOGRAPHS [348 



f A typical larvapod is a fleshy subconical protuberance narrowed toward 

 the distal end, and is usually subdivided into a larger but shorter proximal 

 portion and a smaller but longer distal portion. Sometimes the distal 

 end is dilated and turned mesad, as in Neodiprion (Fig. 82), or the cephalo- 

 ventral angle is pointed, as in Tenthredo. The larvapods are well devel- 

 oped in most of the free-living larvae but in the leaf-miners and 

 fruit-borers they are reduced and smaller. They are very small in the Hylo- 

 tominae and rudimentary in the Fenusinae (Fig. 86) and Schizocerinae, 

 while they are obsolete in Phlebatrophia. The degree of development of 

 the larvapods is closely correlated with the habits of the larva. The 

 larvapods are usually located on the middle of each lateral half of the 

 sternum but occasionally are very close together near the meson, as in 

 Neodiprion. The number of pairs of larvapods present is a convenient 

 character for dififerentiating the subfamilies of the Tenthredinidae. The 

 larvapods often bear a few setae on the cephalic and lateral aspects. 

 The setae, when present, are confined to the mesal aspect. Lack of setae 

 on the larvapods is often a generic character and the number and arrange- 

 ment of the setae is typical of the species. 



Crampton (1919), with good reasons, proposed to substitute the term 

 uropods for the long-used but misleading term prolegs. The term uropoda 

 has been employed by students of the Crustacea in designating the abdom- 

 inal appendages, especially one of the posterior pairs of pleopods, and 

 according to Smith's glossary of Entomology the term refers to "any of 

 the abdominal feet of Arthropoda." These facts indicate the necessity of a 

 distinctive term, and the new term larvapods following the suggestion of 

 Dr. MacGillivray, is used until a happier term is created for these true 

 abdominal appendages of insect larvae. 



Metamerism. — Graber (1890) has shown that the number of somites 

 which compose the body of the larvae of Hylotoma is fourteen exclusive 

 of the head. The first three somites belong to the thorax and the remaining 

 eleven to the abdomen. The ultimate segment, or the telson of the embry- 

 ologists, is difiScult to discern in larvae. It is probably represented by the 

 suranal and subanal lobes of the larvae, but the boundary between this 

 segment and the tenth somite is so obliterated, and the ultimate segment, 

 which is originally much smaller than the preceding somites, is in the 

 larval stage so much more reduced, that it is permissible and also con- 

 venient to speak of the abdomen as being composed of ten segments. 

 For this reason the tenth abdominal somite, which bears the so-called 

 anal prolegs, is designated as the ultimate segment in this paper. It is to be 

 noted that Nelson (1915:111) considers that there are eleven segments 

 and a telson in the abdomen of the embryos of Hymenoptera. In all the 

 larvae of the Tenthredinoidea examined, it is always possible to count 

 ten abdominal segments. The body is usually distinctly segmented. 



