Packard.] ^O [Feb. 3, 



Full-fed Larva. — Length, 20 mm.; breiulth, 7 mm. The body is very 

 thick and stout, nealy one-half as long as broad, the dorsal surface regu- 

 larly convex, being well rounded above, a little wider in front than be- 

 hind. The prothoracic segment, with no tubercles, forming a hood for the 

 head, which is dull amber colored with darker spots. The second thoracic 

 segment with four spinulose fleshy conical tubercles, the dorsal ones 

 slightly larger than the lateral ones. Similar ones on the third thoracic 

 segment, but they are a little larger. On the first and eighth abdominal 

 segments are two very large diverging horn-like processes, and armed with 

 coarse spinules, which like those elsewhere are simple, ending in a slender, 

 stiflF corneous black point. On the last segment is a pair of small tuber- 

 cles and a terminal pair of rust-brown flattened branches of singular 

 spinules. The body is rust-brown, with a livid hue, and the skin is gran- 

 ulated. Abdominal segments 2-7 are pea-green, bordered below with a 

 white lateral line, and enclosing a large dorsal round brown spot bor- 

 dered with whitish. Between the base of the horns is a small pale spot, 

 and behind are two nearly adjoining yellowish-white patches. 



The shape of the stout spines on the tubercles of the full-grown larva 

 is represented by Fig. 3, a, which is, however, one of the smaller spines. 

 A singular spine is represented at Fig. 3, b ; it is clavate, and arises from 

 a papilla situated on the middle of the tubercle near the edge ; such clavate 

 setifi as these are very rare, the only other one observed was situated 

 on the middle of another tubercle below the group of papillse, which 

 extends to the end of the tubercle. A very remarkable spine, and one 

 which we believe is largely concerned in producing the poisonous and 

 irritating eft'ects resulting from contact with the caterpillar of this species, 

 is one situated in scattered groups near the end of the tubercles. A group 

 of three is represented at e. They are not firmly embedded in the cuticle, 

 but on the contrary appear to become very easily loosened and detached, 

 and they probably, when brought into contact with the skin of any ag- 

 gressor, burrow underneath, and are probably in part the cause of the 

 continual itching and annoyance occasioned by this creature. It will be 

 seen by reference to Fig. 3, e' , that the body of the spine is spherical 

 with one large elongated conical spine arising from it, the spherical base 

 being beset with a number of minute, somewhat obtuse spinules. This 

 spine reminds one of an old-fsxshioned caltrop, and a group of them con- 

 stitutes a formidable armature. The cuticle at the end of the tubercles is 

 granulated, each fine projection being the end of a vase-shaped papilla, 

 all being closely crowded together, as at c. The skin of the body between 

 the tubercles is seen to be finely shagreened, an appearance due to the 

 presence of fine clear teeth more or less curved and bent, which arise from 

 a very finely granulated surface, as at d. It will thus be seen to what an 

 unusual extent the diflerentiation of the spines and of the armature of the 

 cuticle itself is carried in this highly specialized form. 



Miss Murtfeldt has called my attention to the variation in the larva; in 

 the length of the tubercles, in the intensity of coloring, and the presence 

 or absence of the cream-colored spots. 



