the Lepidopterous Family Cossidae. 



187 



also (1) the Castniadae by a separate stem; (2) the Zygae- 

 nidae, Limacodidae, Psychidae, and Pyralidae, the first two 

 from a common stem, the exact relationship of the last 

 two being less certain; (3) the Lasiocampidae by a very 

 distinct stem; (4) by yet another stem the Noctuidae, 

 Arctiadae, Liparidae, and Notodontidae, together probably 

 with the Geometridae and Thyatiridae. If so much be 

 admitted, we have already a classification in outline of 

 the Heteroneura. The assignment of the other families of 

 this great assemblage to their positions within this outline 

 must be reserved for another occasion. 



It is apparent that this tl 



phylogeny is based mainly 

 on the neuration. No one 

 is more anxious than I to 

 consider all the characters 

 of all the stages of the 

 Lepidoptera, but the value 

 of all the characters must 

 be carefully weighed. The 

 great problem of phylogeny 

 is the distinguishing of 

 resemblances due to com- 

 munity of descent from 

 those due to evolution in 

 a common direction usually 

 but perhaps not always 

 under the influence of the 

 environment, that is to 

 say, to adaptation to com- 

 mon conditions. Or, as 

 my old teacher, Prof. Ray 



Lankester. used to say in his lectures, we must distinguish 

 homogeny from homoplasy. No better illustration of homo- 

 plastic resemblances can be found than among the larvae 

 of Lepidoptera, for instance, in the resemblance of some 

 Noctuid larvae to those of the Geometridae, of other Noctuid 

 larvae to those of the Bombycine families. Lepidopterous 

 larvae are peculiarly exposed to adaptational modification. 

 They are in no sense embryonic forms, that is to say, 

 forms recapitulating the phylogeny of the insect, but 

 secondary adaptations to a phytophagous existence depart- 

 ing more widely from the primitive insect than do the 

 imagines, and morphologically much degraded, Their 



Fig. 58. — Neuration of the hypo- 

 thetical family Protocossidae. 



