397 



is, tluit we luay expect changes in the pattern to possess a cer- 

 tain systematical value. ïhough this rule is not always adhered 

 to, it generally holds good. 



Of the setal pattern of' caterpillars wc may say what Chapman 

 says of the pupa: "The Lepidoptera certainly cannot be arranged 

 in one line by their pupae, but the Lepidoptera of one line can 

 be arranged by their pupae." In studying the pattern we get 

 tlie inipression of many lines of developnient which often run 

 parallel. This conipletely harmonizes with Handlirscii's opinion 

 and with that of de Meijere. 



Before passing on to the discussion of the families, I wish to 

 devote a few words to the biological signification of the setae, 

 Fracker assumes (1915, p. 38) that the setae are sensory in 

 function. 



Quail(1900) tliinks that the setae of the Hepialidae can open 

 and shut, Wachtl and Kornauth say that the special setae of 

 PsiUira serve to facilitate the spreading of the caterpillars by 

 the wind. Usually it is tliought, however, that the setae serve 

 as a means of defence against enemies, especially Ichneimwnidae 

 and Tachinidae. This opinion has particularly been propagated by 

 Packarü and Poulton. I think I may call it into doubt. The 

 experiments of the last-mentioned writer give us a right to assume 

 that a dense covering of setae or tufts and long pencils, form a 

 means of defence against some vertebrates, but the results he 

 obtained cannot be directly transferred to enemies of the insect- 

 tribe. In structure the eyes of the insects differ so much from 

 those of the vertebrates and are so absolutely different in their 

 sensibility to colours, that we may not treat the problems which 

 here present themselves, from a point of view so anthropomorphic, 

 as for instance Poulton does, in his well-known and interesting 

 book: Colours of animals. On page 87 he says: "A person un- 

 accustomed to the observation of the animals (the light-coloured 

 trout) would certainly fail to detect any trout except the black 

 ones, which were blind and did not vary their colour". I must 

 confess that I fail to see the value of this argument, as I am 



