THE EXTERNAL STRUCTURE OP THE LEPIDOPTEROUS LARVA. 49 



B. SETiE (HAIRS, BRISTLES, ETC.). 



1. — Simple, fine, short or long, macroscopic or microscopic setae, tapering 



hairs, scattered or dense, often forming pencils (many Bombyces, 



Zygaenidae,* Noctuo-Bombyces, Apatelae). 

 2. — Glandular hairs, truncate, spindle-shaped or forked at the end, and 



secreting a more or less viscid fluid [many Notodonts in Stages 1 and 2 ; 



many butterfly larvse; Pterophoridae (in last stages)]. 

 3. — Long spindle-shaped hairs of Apatelodes (Apatela americana), and 



Tinolius eburneigutta. 

 4. — Flattened, triangular hairs in the tufts, or on the sides of the body of 



Gastropacha americana, or flattened, spindle-shaped scales in the 



European G. quercifolia. 

 5. — Spinulated or barbed hairs (most Glaucopides, Arctians, Lithosians, 



Liparids and many Bombycids). 



C. — Pseudo-tubercles. 

 1. — Filamental anal legs (stemapoda) of Centra and Heterocampa marthesia. 

 2. —The long suranal spine of Platyptericidae. 



Before leaving our consideration of the hairs of larvse, it may be 

 well to mention the spathulate hairs of Jocheaera alni. These are 

 usually erect and conspicuous, but in the adult stage are spread some- 

 what laterally. Chapman gives them as measuring, in the 4th larval 

 skin: on pro-thorax, 3 J mm., on 5th abdominal, 1£ mm., on 9th 

 abdominal, 2-| mm. ; in the 5th larval skin, on the same segments 6, 

 3^ and 4 mm. respectively, and in the 6th larval skin (extra moulter), 

 7, 4, and 4-| mm. respectively. The larva of EtUricha quercifolia and 

 those of other species possess remarkable scale-like hairs, as mentioned 

 above by Packard. 



The study of the newly-hatched larva is one of the most important 

 factors in considering the phylogeny of the lepidoptera, for it happens 

 that many species which have the most specialised adult larvae hatch 

 in a very generalised condition, and hence, comparison of the tubercles 

 in the newly-hatched larvae, with the more specialised structures that 

 replace them afterwards, gives many valuable clues to the origin of 

 the complicated structures of the adult. From this, it would appear, 

 that the more primitive arrangement of the five chief tubercles and setae 

 occurring on the abdominal segments, is such that the three tubercles 

 above the spiracle exist as the anterior trapezoidal, posterior trapezoidal, 

 and supra-spiracular tubercle, respectively, whilst the sub- and post- 

 spiracular tubercles are both placed beneath the spiracle. Dyar 

 remarksf : — " Curiously enough, the most generalised condition is ex- 

 hibited in the first stage of the butterflies (Rhopalocera). This is to be 

 accounted for by the fact, which was brought out by a comparison of the 

 first stage of such genera as Danais and Grapta, with their later stages, 

 viz., that the armature of the butterfly larva is not developed mainly 

 from the primary tubercles, but almost entirely independent of them." 

 This is certainly too sweeping an assertion to comprise the facts re- 

 lating to the armature of the Vanessid and Argynnid larvae, and pro- 

 bably some others. In many cases there can be no doubt that the 

 armature is frequently developed from the primary tubercles, often, of 

 course, with certain stages of the evolution left out. In some the process 

 of development is comparatively simple, as may be seen, if the larva be 



* As used in America, this = our Euchromiidae, which are Arctiids, not the family 



British lepidopterists call Zygaenidae. 

 f " Additional notes on the classification of Lepidopterous larvse," Trans. Neiv York 

 Acad. Sci., xxv., p. 52. 



D 



