270 NATURAL HISTORY OF AQUATIC INSECTS CH. 



cocoon in a very Trichoptcrous manner.^ These 

 considerations are of various degrees of importance, 

 and some of them would not carry much weight with 

 the systematist. Those naturalists who, like the 

 writer, are compelled by their ignorance of systems 

 to take all their views on such matters from other 

 people, will acquiesce in Mr. McLachlan's opinion 

 that in any linear arrangement the Trichoptcra and 

 Lcpidoptera must not be widely separated. 



It might be supposed that Caddis-worms, being 

 immersed in water as well as protected by a case, 

 would be free from the destructive attacks of Insect- 

 parasites. Mr. McLachlan has, however, mentioned a 

 Dipterous parasite which infests Limnophilus, one of 

 the Caddis-worms, and a short account of an 

 Ichneumon (Agriotypus), which preys upon another 

 Caddis-worm, is given in the section on Aquatic 

 Hymenoptera (p. 223). 



Many of the contrivances of Insects are not con- 

 fined to a single order. The singular habit of laying 

 eggs in living larvae is shared by Hymenoptera 

 and Diptera ; Lepidopterous, Dipterous, Hymen- 

 opterous, and Coleopterous larvae mine in the thick- 

 ness of a leaf; Hymenoptera, Diptera, Coleoptcra, 

 and Rhynchota practise the art of making galls on 

 plants ; societies with a common dwelling exist 

 among Hymenoptera (Bees, Wasps, and Ants), and 

 also among Pseudo-neuroptera (White Ants) ; the 

 Dipterous Leptis vermileo imitates the pit-falls of the 

 Ant-lion (Neuroptera). Hence it is in accordance 

 with the great adaptability of the Insect-organisation 

 ' I-^r. T. A. Chapman, Trans, Enf. Soc, 1893, p. 255. 



