DIPTEROUS LARVAE 607 



In the Diptera, which are the most highly specialized of insects, 

 the maggot or vermiform shape, and absence of any legs, prevails 

 throughout the order, though the eucephalous larvae show their 

 origin from a primitive eruciform type of larva. The highly 

 specialized larvae of the Culicidse and Simlidse are undoubtedly 

 related to the earliest and most generalized types, while the maggots 

 of the parasitic flies (Tachinidse) and other muscids are later degra- 

 dational forms, and the result of adaptation induced, as in the 

 previous cases, by a sedentary or parasitic mode of life, living 

 as they do immersed in an abundance of rich nitrogenous food, 

 with the result that the mouth-parts have become atrophied by 

 disuse, while the limbs have become entirely aborted, though the 

 thoracic imaginal discs develop normally in the embryonic or pre- 

 larval stages. 



It appears, therefore, highly probable that the metamorphoses 

 of insects are the result of the action of change of conditions, just 

 as the polymorphism of Termites is with little doubt the result of 

 differences of food and other conditions. These matters will be 

 farther discussed under the head of Causes of Metamorphosis. 



LITERATURE ON ANCESTRY OF INSECTS, ETC. 



Muller, Fritz. Fur Darwin, 1869, pp. 144, 67 Figs. 



Brauer, Friedrich. Betrachtung ueber die Verwandlung der Insekten im Sinne 

 der Descendenz-Theorie. (Verhandlung d. k.k. zool. bot. Gesell. Wien., 

 1869, 1 Taf., pp. 1-20.) 



Packard, A. S. Amer. Naturalist, iii, p. 45, March, 1869. 

 Proc. Boston Soc. Nat. Hist., xiv, 1870, p. 61. 

 Amer. Nat., iv, Feb. 1871, p. 756 ; v, 1871, pp. 52, 567. 

 Embryological Studies. (Memoirs Peabody Acad. Sc. Salem, 1871-72.) 

 Our common insects, 1873, Chapter on Ancestry of Insects, pp. 175-178. 

 - Third Report U. S. Ent. Commission, 1883, pp. 295-304. 

 Lubbock, John. On the origin of insects. (Journ. Linn. Soc., London, xl, 1873.) 



Origin and metamorphoses of insects. (Nature, 1873 [in book form, 



1874], pp. 108, 66 Figs.) 

 Mayer, Paul. Ueber Ontogenie and Phylogenie der Insekten. (Jena. Zeitschr. 



Wissens., x, 1876, pp. 125-221, 4 Taf.) 



Hyatt, A., and Arms, J. M. Insecta. (Bost. Soc. Nat. Hist. Guides for science- 

 teaching, viii.) Boston, 1890, pp. 300, 13 Pis., 223 Figs. 



