1917.1 227 



pale and, instead of being opaque (and black), the cranium when mounted 

 is transparent, with some ii-regular lines and a number of small circular, hemi- 

 spherical pits, each with a minute circle at the bottom. In P. aterrima the 

 head is similarly black and solid in the last feeding instar, and in the final 

 instar is transparent, but has no hairs. It has pits very like those in R. micans, 

 but the intermediate areas are occupied by plates of much the same size as 

 the cups, and separated from each other by narrow channels. The skin in 

 P. aterrima in this last instar has no longer the sharp skin-points of the 

 preceding instars, but has merely a tessellation of cells ; in the position 

 of the black points the area is marked out by the tessellation being rather 

 more plainly marked, in a definite oval area, the central cells being the 

 larger. In the skin structure in this last instar the two species, previously so 

 diflerent, are now very much alike. 



It is curious that the presence of hairs in the imago of Plujmatocera 

 aterrima, which so easily distinguishes it from Hhadinoceraea viicans, obtains 

 also in the larva, the head having hairs and the skiu-points being sharp. 



Cameron refers to various sawflies changing their colour previous to 

 moving off to find a place for pupation, but he says little as to the change 

 occurring by means of a moult, after which no food is eaten. In specific 

 descriptions he does not mention whether this special moult does or does not 

 occur. I do not think the circumstance is noted in detail by any Enslish 

 authority, but piy ignorance of the literature of sawflies is, no doubt, the 

 reason I cannot refer to any such record. 



There is, of course, little doubt that the change has reference to a search 

 for a place in which to make a puparium, just as a similar change (but without 

 a moult) is so well known to occur in many Lepidoptera, and, no doubt, makes 

 the larva much less conspicuous. But these sawfly larvae pass the winter in 

 their puparia and only pupate in the following spring, and it is probable that 

 the change of colour being acquired by a moult has some reference to acquiring 

 a smoother and more uniform coat, which will be more comfortable and 

 especially, probably, will not permit so much evaporation and so avoid, 

 desiccation. 



There is another difference between the two instars in the size of th& 

 spiracles, which are distinctly larger in the pupating thaa in the feeding one. 

 This difference is much more pronounced in Lophyrus pini, in which the 

 hibernating spiracles are nearly twice the diameter of those in the feeding 

 instar. This may have some reference to the unquestionable fact that in, 

 the cocoon there is no need to defend the spiracles from any foreign objects^ 

 but it probably also refers in some way to more ready use of the restricted, 

 supply of air. 



Mr. Morice tells me of the larva of a species of Periclista (probably meluno^ 

 cephala) whose larva has abundant bifid spines but on this last moult gets rid 

 of them altogether and goe.? down with a smooth skin. Lophrjrus pini makes 

 a similar moult with little change in appearance. 



In L. pini, to whose spiracles I have already referred, in the last 

 feeding stage, each segment has a considerable number of tubercles, each con- 

 sisting of a little upright spine with rounded top, and the black marks are 

 apparently actual cliitiuuus plates. In the pupating instar there are no spines, 



