NO. 6 



INSECT ABDOMEN — SNODGRASS 



87 



other muscles in the base of a thoracic leg (fig. 38 B, C, d, e, f, g) 

 are coxo-trochanteral and coxo-femoral muscles, representatives of 

 which are entirely absent in the abdominal legs. On the other hand, 

 the plantar muscles of the abdomen have no evident counterparts in 

 the thorax. 



The general parallelism between the muscles of the abdominal ap- 

 pendages and those of the thoracic legs shows that the musculature 

 of the prolegs in the mature caterpillar is, as Eastham says of the 

 musculature in the embrvo, " comparable to that of the thoracic limbs 

 though of a weaker order." Moreover, if the musculature has any 



Fig. 38. — Body muscles of a thoracic leg of a caterpillar. 



A, external body muscles and leg muscles of ventral area and right half of 

 metathorax of Malacosoma miicricana. B, basal muscles of right metathoracic 

 leg of same. C, coxal and coxo-trochanteral muscles of right mesothoracic leg 

 of Estlgmcnc acraca. 



bearing on homologies in the segments of the appendages, it shows 

 that the suprapedal lobes of the l)ody wall above the abdominal limbs 

 are the subcoxae (fig. 37 A, D, Sex), and that the principal parts 

 of the legs are the coxae (Cr). The plantae of the abdominal ap- 

 pendages, however, have no evident homologues in the thoracic legs, 

 nor do their muscles correspond with any of the muscles of the legs 

 in the thorax. 



The nature of the planta becomes clear when we compare an ab- 

 dominal limb of a caterpillar (fig. 37 D) with an abdominal appendage 

 of the Corydalns larva (fig. 36 C, D). A striking resemblance is 



