URBICOLA COMMA. 177 



The head now exhibits two ochreous vertical parallel lines down the 

 crown, and an ochreous y^-marking above the mouth ; otherwise the 

 form and structure of the larva is similar to the earlier stages. Fifth 

 instar (July 9th) : Fullgrown, measuring 28mm. in extreme length 

 while crawling. The head is large and similar to previous stage in 

 colour. The prothorax very small, elastic, and retaining the black 

 collar of former stages ; the following segments gradually increase in 

 size to the 3rd abdominal, and taper from the 6th to anus. The entire 

 surface is densely sprinkled with minute shining black warts, each 

 emitting a tiny amber-coloured spine or seta with a cleft knobbed apex; 

 those on the ventral surface are simple spines and rather longer. The 

 skin is also covered with fine regular granulations which are dusky in 

 colour, and exceedingly minute. Besides these there are, sprinkled 

 over the whole surface, very small spiracle- like processes, the largest 

 being situated on the claspers (which have a shining whitish film-like 

 surface stretched over the centre), and one on each segment below the 

 true spiracle, which is conspicuous, black and shining. The 7th and 

 8th abdominal segments have the anterior half of the ventral surface 

 covered with a rough white granular waxy substance* (Frohawk). 



Larva. — The prothorax has a transverse black plate, about 4mm. 

 across, and about 0'4mm. wide; from the appearance of the fracture, 

 in casting the skin for pupation, there is no very definite dorsal suture; 

 it carries several hairs, as well as certain ocellations that may be lenticles 

 or merely bases of hairs that have been lost ; it has a paler line with 

 darker margins, that seems to be a groove or channel passing across 

 about one-third from the posterior margin ; there is a paler band near 

 each extremity, marking off a terminal area, very similar to what occurs 

 in many Psychids ; the whole surface is finely spiculated precisely like 

 the rest of the cutaneous surface. Just beyond the end of the plate is 

 the dark spiracle, more prominent, but not larger, than that of the 8th 

 abdominal segment, the other abdominal spiracles are smaller and much 

 less prominent, but all appear to have much the same structure. This 

 prothoracic spiracle is about 025mm. long, 0-15mm. across, and about 

 O06mm. high; it has a very narrow outer oval ring, then the chitin of 

 the spiracle proper rises, maintaining the same diameter to the stated 

 height of about O06mm., and then curves inwards for about OOSmm., 

 leaving the lumen of the spiracle ; it, however, occupies a good part of 

 this space by chitinous processes, much like the pectinations of an antenna, 

 and similarly clothed with fine hairs ; these proceed from the whole 

 margin, but chiefly from the sides, most of the central ones being 

 parallel, they just do not meet in the centre; on the thoracic spiracles, 

 they are about twenty in number on each side. The abdominal spiracles 

 are of precisely the same structure, but are only 0*1 5mm. long, are nearly 

 flat and have about fifteen gills on either side. Halfway between 

 the spiracle and the first legs are a pair of lenticles side by side ; these 

 are dark rings about 0*09mm. in diameter, with a pale structureless 

 diaphragm (on a higher magnification the membrane is seen to be 

 very finely granulated, granulations less than OOOlmm.). Some of the 



* Staudinger notes (Stett. Ent. Zeit., 1861, p. 357), in his description of the 

 full-grown larva taken in nature : " The most extraordinary feature of the larva is a 

 snow-white exudation, which extends almost entirely over the 10th and 11th 

 segments ventrally, rather thick, scaly in form and sticky. Under considerable 

 heat it melts like wax and loses the white colour completely." 



