60 METAMORPHOSIS 



abdominal appendages j)resent varies from eight in Phcenoserphus, 

 to ten in the Figitidai (Fig. 34), and twelve in Ihalia. 



3. The Oligopod Type. The oligopod type, in its most highly 

 developed condition, is represented by the so-called campodeiform 

 larva of many Coleoptera and Neuroptera. It is eminently active, 

 with highly developed locomotory and sensory organs, and has, 

 in the past, usually been regarded as the most primitive type of 

 insect larva. Almost every stage of adaptive modification and 

 degeneration is exhibited, among different insects, between this 

 highly developed type and the legless phase dealt with in the next 

 paragraph. 



4. The Apodous Type. The apodous type, which is devoid of 

 all true locomotory appendages, appears to have been derived, in 

 the majority of cases, from the oligopod phase as the result of 

 degeneration. Larvae of this type are characteristic of Diptera 

 and all the Hymenoptera Apocrita ; they are also prevalent in 

 certain families of Coleoptera, besides occurring as a rare condition 

 in leaf- mining Lepidoptera. 



Among Diptera the general suppression of body-appendages, 

 from all stages in their ontogeny, has resulted in the antecedent 

 protopod and polypod phases becoming largely obliterated. 

 Keilin (1915) has shown that three pairs of sensory papillae are 

 present in the larvae of this order, and are in direct relation with 

 the developing imaginal leg-buds, thus occupying the positions of 

 ancestral thoracic legs. These sensory papillae appear to be the 

 transformed vestiges of former thoracic limbs, and their presence 

 points to the conclusion that Dipterous larvae are to be regarded 

 as highly specialised derivatives from the oligopod type. 



In all the higher Hymenoptera the prevalent larval type is 

 apodous. Among the Aculeata it persists through all instars, 

 while, as has already been shown, in certain of the Parasitica it is 

 preceded by earlier phases. The apodous type in this order is 

 most probably a derivative of the oligopod phase, as in Diptera. 

 In support of the contention it may be mentioned that vestiges, 

 in the form of papillae, of what appear to be the remains of thoracic 

 appendages have been detected in Polysphincta and certain other 

 of the Ichneumonoidea. Furthermore, in the Tenthredinoidea a 



