THE GENERAL SUBJECT 61 



long series of transitional forms are traceable from typical poly pod 

 types, through various phases of reduction, to oligopod types, 

 until a completely apodous condition is attained. Thus, in the 

 Xyelidae their polypod larvae retain nine pairs of abdominal 

 appendages, while among the Tenthredinidae (sens, str.) this 

 number suffers reduction. In the Pamphiliidae, Cephidas and 

 Siricidse, abdominal appendages have atrophied and their larvae 

 are oligopod ; the thoracic limbs are never well developed and 

 exhibit varying degrees of reduction towards the apodous con- 

 dition. In Oryssus the latter phase becomes evident, the thoracic 

 limb-rudiments having atrophied. The legless condition of the 

 larva in this genus is correlated with the unique parasitic life that 

 is unknown elsewhere among the Symphyta. 



Among Coleoptera an apodous larval type has been indepen- 

 dently acquired among different families. It is characteristic of 

 the majority of the Rhynchophora, besides occurring in certain of 

 the Buprestidae and Cerambycidae ; in Cercyon, in the Elaterid 

 sub-family Eucneminae and in the Bruchidae. In the last- 

 mentioned family the apodous condition may be preceded by 

 oligopod instars, while among the Curculionidae the last remnants 

 of thoracic limbs are retained as sensory protuberances in Hypera 

 (Phytonomus) according to Perez (1911). In Coleoptera, therefore, 

 evidence points to the apodous type being . derived from the 

 oligopod, and almost every transition between the two may be 

 found, sometimes in members of the same family. In Lepidoptera 

 the leaf-mining genera Phyllocnistis and Eriocrania are apodous, 

 but, unlike the preceding examples, the legless condition appears 

 to have been directly derived from the polypod phase. 



General Remarks on Insect Metamorphosis 



It will be apparent that Berlese's theory is in accordance with 

 the general facts of ontogeny and phylogeny. Criticisms, however, 

 may be raised wherever a given larval type does not appear to 

 conform with his premises and deductions. Due reflection will 

 show that it is obviously improbable that every form of larva that 

 issues from the egg will be in a stage exactly comparable with one 

 or other of the embryonic phases alluded to. Intermediates are 



