Phyletic Parallelism in Metamorphic Species. 491 



do not serve for the reduction of food but only for 

 fastening the whole body. With the jaws and 

 their muscular system there likewise disappears 

 the necessity for a hard surface of attachment, 

 i.e. a corneous head. 



The mode of life of the larvae of the gnat- 

 type is quite different in most points. The 

 majority, and indeed the most typically formed of 

 these, have to go in search of their food, whether 

 they are predaceous, such as the Culicidte and 

 many of the other Nenwcera (Cordhra, Simulium), 

 or whether they feed on plants, which they in some 

 cases weave into a protective dwelling tube (certain 

 species of Chironomus). Many live in water and 

 move with great rapidity ; others bury in the 

 earth or in vegetable substances ; and even those 

 species which live on fungi sometimes wander 

 great distances, as in the well-known case of the 

 " army worm " where thousands of the larvae of 

 Sciara Thonue thus migrate. 



Now the two types of larvae correspond gene- 

 rally with the two large groups into which, as it 

 appears to me correctly, the Diptera (genuina) are 

 as a rule divided. In this respect there is there- 

 fore an equality of form-relationship the group- 

 ing is the same, and the incongruence depends 

 only upon the form-divergence between the two 

 kinds of larvae being greater than between the 

 two kinds of imagines. 7 



' I am familiar with the fact that the two sub-orders of 



