10 BKITISH LEPIDOPTEEA. 



still remained comparatively narrow, when, suddenly the exuviae fell 

 away disclosing the two perfect filaments. Thus, at 12.20 a.m., was 

 this moult completed, having, from the rupture of the skin to the final 

 riddance, occupied one hour and a quarter." 



Stainton noticed on September 16th, 1886, a batch of larvae of 

 Phalera bucephala already laid up for their last moult. On the 17th a 

 silken carpet had been spun, and they rested quite immovably through 

 the 18th, 19th, and 20th (when, however, one example was noticed 

 throwing its head from side to side) . The first moult took place on 

 September 21st soon after noon, and all the batch but one or two 

 individuals had moulted by the morning of the 22nd, but none fed 

 until the afternoon of that day. Stainton notes, concerning the 

 actual moult, that " the gradual retirement of the old skin towards 

 the anus seemed to be almost a self-acting motion, to which the larva 

 contributed but little till the time came for extricating the anal 

 extremity from the old skin." He says that " the old heads were 

 completely detached from the other part of the skin, and fell down 

 separately as the moulting progressed." 



As we have already hinted, the formation of the new skin beneath 

 the old one is due to the secretion of the structureless chitinous layer 

 by the cells of the hypodermis, by the process of histogenesis. Packard 

 says that " these cells at this time are very active, and the formation 

 of the new layer of chitin arrests the supply of nourishment to the old 

 skin, so that it dries, hardens, and, with the aid of the fluid thrown out 

 at this time, separates from the new chitinous layer secreted by the 

 hypodermis." 



That this fluid exists between the two layers is evident. We have 

 seen the new hairs of Arctia caia and Apatela aceris quite moist when 

 first set free from the old skin. Chapman says that "the fluid is 

 related to that which hardens into the dense pupal case, and also 

 hardens in a less degree the skin of the larva." He supposes that " it 

 must contain some chitin in a soluble form, for if a newly-cast larval 

 skin be taken, there is no difficulty in extending the shrivelled mass to 

 its full length and dimensions, but, if a short time elapses, this chitin 

 hardens and the skin cannot be extended after soaking in -water, 

 alcohol, ammonia, or any other solvent experimented with." 



There is no doubt that the growth of the setae and hairs on the 

 new cuticle likewise serves to loosen the overlying skin which has to be 

 exuviated. 



It would appear that there is no essential difference between the 

 exuviation of the last larval skin that sets free the pupa and those 

 preceding it. Gonin states that during pupation the outside of the 

 pupa, especially the parts of the head and throax, is coated with a viscid 

 liquid "secreted by special thoracic glands." Subsequently it was 

 determined that the fluid was not secreted by these special cells found 

 on the thoracic segments, but was distributed all over the surface, and 

 Bugnion considered it to be a secretion of the whole surface of the 

 hypodermis when the cells were still soft and not yet hardened by 

 contact with the air. 



There is considerable variation in the number of moults that 

 lepidopterous larvae undergo, and even in the number of moults in the 

 same species, the difference sometimes being sexual, e.g., Notolophus 

 antique, in which the female larva undergoes a moult more than that 



