137 



18, that we may expect changes in the pattern to possess a cer- 

 tain systeniatical value. Though this rule is not always adhered 

 to, it generally holds good. 



Of the setal pattern of caterpillars wo may wty 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 

 the impression of many lines of development which often run 

 parallel. This completely harmoni/.es with Hanih.iksch's opinion 

 and with that of i>e Meijkrk. 



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

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

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

 function. 



Quail (1900) thinks that the setae of the llepialidae can open 

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

 Psilum serve to facilitate the spreading of the caterpillars by 

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

 as a means of defence against enemies, especially Ichneiimonidae 

 and Tachinuiae. This opinion has particularly been propagated by 

 Packard and Poultox. 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 Poultox does, in his well-knowm 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 



