441] LARVAE OF THE TENTHREDINOIDEA—YUASA 123 



like. The legs are very small compared with the size of the body. The 

 Tenthredinidae present a series of conditions which illustrate beautifully 

 cases of modification both by reduction and addition. The typical, well- 

 developed, five-segmented legs undoubtedly represent the normal sequence 

 in development from the condition found in the Xyelidae. The apparently 

 six-segmented condition of the Hylotominae, four-segmented legs of the 

 Fenusinae, and three-segmented condition of the Schizocerinae, together 

 with the development of distal fleshy lobes in the first- and last-named 

 subfamilies are cases of specialization. The fact that the specialization 

 by reduction of segments has not proceeded at the same rate in the last 

 two subfamilies is indicated by the difference in the structure of the 

 segments. It is interesting to note that the prothoracic legs of the Schizo- 

 cerinae still retain four segments in spite of the fact that in the two caudal 

 pairs the number of segments has been reduced to three. The osculant 

 genus Phlebatrophia is unique among all other Tenthredinidae in having 

 the legs modified to such an extent as to lose all resemblance to normal 

 segmented legs. They have become mere fleshy, indistinctly segmented, 

 clawless protuberances. In this character this genus resembles highly 

 specialized families such as the Cephidae and its allies. The Cephidae, 

 Xiphydriidae, and Siricidae represent a series of modifications in which the 

 changes have resulted in fleshy, vestigial, entirely clawless legs with or with- 

 out indication of segmentation. Judging from the size and degree of 

 segmentation, the Xiphydriidae is more generalized than the Siricidae 

 and more specialized than the Cephidae. The Oryssidae is entirely apo- 

 dous, and the fact that it is parasitic on buprestid larvae leaves no doubt 

 as to its extreme specialization. 



The larvapods are considered as true appendages of the abdominal 

 segments. Their presence is highly significant from a phylogenetic point 

 of view. The larvae of the Tenthredinoidea are divisible into two types 

 according to the presence or absence of the larvapods. The Xyelidae 

 and Tenthredinidae represent the type with polypodous larvae and the 

 other five families represent the type with apodous larvae. In the first 

 group the Xyelidae possess the maximum number, or ten pairs, of larva- 

 pods, while the Tenthredinidae are provided with six to eight excepting 

 certain specialized genera which possess very vestigial or no larvapods. 

 It has not been possible to determine the reason for the invariable absence 

 of larvapods upon the first and ninth uromeres in the Tenthredinidae. It 

 may be that the same mechanical factors which have caused the fusion 

 of anal larvapods in boring larvae like Caulocampus are also responsible 

 for this condition. The size and, to some extent, the structure and position 

 of the larvapods vary within the Tenthredinidae as in the Schizocerinae, 

 Hylotominae, and Fenusinae. It is interesting to note that the gall-making 

 genus Pontania retains normal larvapods as well as thoracic legs, while the 



