20'2 THE ENTOMOLOGIST. 



In the case of the last three they are very slender, and probably 

 would not penetrate the skin. The short hairs behind the hump 

 in Acromjcta tridens are similar, but the long hairs in this species, 

 and in A. psi and A. rumicis, are quite smooth. Apparently, in 

 the case of D. pudihunda, it is the tussock hairs which are most 

 harmful. These are very sharp and stiff, with extremely long 

 spines closely set. Orgyia antiqua possesses similar spines, 

 but they appear less strong, and probably their absence of 

 effect on Mr. Carter is due to this. In D. fascelina the spines 

 are much longer, but appear thinner, and stand out more from 

 the shaft. 



The hairs in Arctia caia, A. villica, Acrouycta aceris, and 

 Malacosoma neustria are alike in possessing a small swelling just 

 before the hair terminates in its sharp point. In the first three 

 there are small sharp spines directed forwards. M. neustria, 

 however, has a very few minute spines with wide bases directed 

 at right angles to the shaft. In all these insects, if the hair 

 punctured and broke off, it would with difficulty be extracted, 

 but they do not appear to possess much penetrating power. 



Most interesting, however, were the hairs of Porthesia auriflua. 

 I shook a cocoon of this species on to a slide, and found numbers 

 of extremely minute hairs. They were very fine and short, and 

 under a high power of the microscope showed very close set lines 

 of backwardly directed short spines or barbs. The base in all 

 cases terminated in two larger divergent curved spines. In the 

 larva these hairs exist in a thick tuft on the fifth segment, and 

 are easily pulled out. Apparently the evil effects of P. auriflua 

 are due to these, and not to the long hairs. I could only obtain 

 one cocoon of P. chrysorrhoea, and this appeared almost free from 

 hairs, the few present being typical long spiny ones. 



The long hairs in Lasiocampa quercm, L. ruhi, and Odonestis 

 potatoria are quite smooth. The small hairs, however, though 

 appearing smooth under low power, were found to be studded 

 with rows of minute backwardly directed spines. In the cocoon 

 these stand out, and with their stiffness and sharp point readily 

 penetrate the finger. Though all these hairs are apparently 

 hollow, they are generally full of air-bubbles, and there is no 

 visible exit for any poison which might be secreted. Since they 

 are equally virulent in the cocoon, this explanation of their 

 action seems unlikely to be correct. And though the different 

 effects of the hairs on Mr. Carter and others seem to point to a 

 specific poisonous action, the hairs are chitinous, and chitin is a 

 harmless body. 



The rapidity of the action, also, is difficult to explain on any 

 other grounds. The larvae possessing smooth hairs, such as 

 some Acronyctas, Leucoma salicis, Saturnia carpini, and Poscilo- 

 campa populi appear to be harmless to any skin, however sus- 

 ceptible. In the spiny haired larvae the detach ability of the 



