494 Studies in the Theory of Descent. 



The Dipterous maggots have evidently 

 descended from which a larval form possessed a 

 horny head with antennae and three pairs of jaws, 

 but which had no appendages to the abdominal 

 segments ; they are therefore ordinary Dipterous 

 larvae of the gnat-type which have become modi- 

 fied in a quite peculiar manner and adapted to a 

 new mode of life, just as the grubs of the Hymen- 

 optera are larvae of the saw-fly type, which have 

 become similarly transformed, although by no 

 means in the same manner. The resemblance 

 between the two types of larva is to a great 

 extent purely external, and depends upon the 



iii. Heft 2. 1876. [Some remarks by F. M. Balfour on 

 the origin of certain larval forms have already been quoted in 

 a previous note (p. 485). This author further states : "The 

 fact that in a majority of instances it is possible to trace an 

 intimate connection between the surroundings of a larva and 

 its organization proves in the clearest way that the characters 

 of the majority of existing larval forms of insects have owed their 

 origin to secondary adaptations. A few instances will illustrate 

 this point : In the simplest types of metamorphosis, e.g. those 

 of the Orthoptera genuina, the larva has precisely the same 

 habits as the adult. We find that a caterpillar form is assumed 

 by phytophagous larvge amongst the Lepidoptera, Hymenop- 

 tera, and Coleoptera. Where the larva has not to go in search 

 of its nutriment the grub-like apodous form is assumed. The 

 existence of such an apodous larva is especially striking in 

 the Hymenoptera, in that rudiments of thoracic and abdominal 

 appendages are present in the embryo and disappear again in 

 the larva. ... It follows from the above that the develop- 

 ment of such forms as the Orthoptera genuina is more primi- 

 tive than that of the holometabolous forms, &c." Comparative 

 Embryology, vol. i, p. 352. R.M.] 



