rackard.] O^ [Feb. 3, 



being caterpillars which have lost by disuse their abdominal legs, the tho- 

 lacic ones being greatly reduced in size, while by their sluggish disposi- 

 tion, by their slug-like, slow gliding mode of progression, and by the pecu- 

 liar coloration of such forms as the larval lleterogenea, which mimics the 

 red, swollen spots on the leaves of various trees, particularly the oak, 

 chestnut, wild cherry etc., we have, as the result of gradual modification 

 brought about by adaptation, perhaps the most strange and bizarre type 

 of Lepidopterous larva in existence. 



Thus, as a result of adaptation, probably brought about by a series of 

 causes unlike those affecting any other caterpillars, we have larvae wliich, 

 as in that of L. faseiola and also the larvaj of Packardia, are entirely green, 

 oval in form, and which we have noticed might easily be mistaken for a 

 fold or bend in a leaf. These smooth bodied, unarmed slug-worms are 

 protected (1) by their oval shape, the expanded edges of the body appear- 

 ing to merge into the surface of the leaf; (2) by their sluggish almost im- 

 perceptible gliding motions ; (8) by their pale pea-green gi'ound color, with 

 faint yellowish or reddish shadings on the more exposed ridges and pro- 

 jections of the body. These and other wholly green ones may have been 

 eliminated during the struggle for existence from the earlier, tuberculated 

 genera by their resemblance to green galls or swellings on the surfaces of 

 leaves. That the larvae of Heterogenea, such as U. flexuosa and II. testacea, 

 are wonderfully similar to the red dipterous or aphidid galls on oak and 

 other leaves was first suggested to us by the late Mr. S. Lowell Elliott,* 

 and since then we have frequently verified his observations, and been 

 struck with the wonderful resemblance between tliese larvae and the 

 small reddish and greenish galls wliich appear late in summer on the 

 leaves at the time when the larvae themselves become fully grown. These 

 forms being thus protected from observation and harm, do not need the 

 armature of the other group, the tubercles and spines have disappeared 

 through simple disuse , while being without poison-bearing spines, they 

 have also lost by disuse the bright colors and conspicuous spots of the 

 armed genera. On the other hand, the larvae of Adoneta, Empretia, 

 Euclea and allied forms, with their remarkabh'^ bright colors and mark- 

 ings, and poison-bearing tubercles, feed conspicuously, the warning colors 

 and showy ornamentation repelling the attacks of birds. We are inclined 

 to the belief that the armed slug-worms were the earlier, from the proba- 

 bility that in the Coleoptera the earliest and most generalized groups were 

 IheStaphylinidae, and the carnivorous Carabidae, and allies, while the later, 

 most extremely modified forms were the Weevils and Scolytidae, in which 

 the larvae are footless. In the Diptera also it is not improbable that those 

 families 'with the most perfectly developed larvae, such as the Culicidae 



* Compare the remarks of Mr. Poiilton on the meaning of the peculiar method of pro- 

 gression in the larvoe of Cochliopodid;c in Trans. Ent. Soc. of London, 1888, 5'Jl , wherein he 

 states that Mr. Tate could not remember any object which the larvtc of H. asdla resem- 

 bled. Mr. Poulton remarks that they "may suggest the appearance of some kind ot gall 

 on the surface of the leaf." 



