114 ME. E. P. STEBBING ON THE LIFE-HISTORY OF 



yellow at first, darkening to a yellow-umber or madder-brown in a few bours after being 

 laid. About 30-40 are laid by tbe female, a day being spent in this operation, the 

 female subsequently dying and her shrivelled skin remaining as a partial protection to 

 the eggs beneath the cottony mass. PI. 22. figs. 3 and 4 show the apterous female 

 egg-laying and with the eggs completely laid, the figures in both instances being drawn 

 from life under the microscope. The majority of the spring larvae of the first generation 

 are apterous females and lay their eggs in the third and fourth week in May. 



A small proportion of the spring larvae develop into a winged generation of individuals 

 (the Sexuparj; ?) on the Silver Fir. 



The full-grown larvae, which will produce the winged insect, are easily recognisable on 

 the Siver Fir needles under a lens, owing to their narrower elongate elliptical shape and 

 to the light yellowish-brown swellings visible on either side of the thoracic region 

 (fig. 6). The skin of this larva bursts open at the head and thoracic end and the winged 

 insect with its wings furled in two little bundles on the thorax crawls out. The wings 

 uncurl, soon dry and stiffen in the sun, and become functional (fig. 7). 



I have not been entirely able to settle the movements of the whole of this winged 

 portion of the spring generation of larvae. It may be that some of them fly off to the 

 Spruce to oviposit there, but I have not as yet been able to find any individuals of this 

 winged generation on the Spruce. 



They are to be found not unfrequently on the Silver Fir needles with their proboscides 

 buried in the tissue of the under surface of the leaf. A proportion of them, I think, 

 undoubtedly lay eggs on the under surface of the Silver Fir needles in a similar manner 

 to the apterous females, and, this being so, the speculation arises as to why they should 

 have acquired wings. It is true that the possession of alar appendages enables them to 

 migrate from the needles upon which they were reared to others in the neighbourhood 

 which are not occupied by numbers of egg-masses, and this may be the reason for a 

 proportion of the young larva? growing into a winged generation. I think, however, the 

 most reasonable surmise is that a percentage of these migrate thus early in the year to 

 tbe Spruce. If this is the case, they form the true Generation IV., the Sextjpaile, or 

 the first portion of it, of the year, provided the eggs they lay upon the Spruce give rise 

 to a sexual generation. Further observations by fellow- workers on this interesting 

 portion of the life-history will settle this point definitely. 



That a portion of the winged generation would seem to remain on the Silver Fir I have, 

 I think, jn-oved by the following observations : — On the 24th May I described a winged 

 living individual under the microscope, and kept it under observation on the 25th and 

 26th. On the 24th the insect had merely issued from the last larval covering, acquired 

 its functional wings, and taken up its position head downwards with its proboscis buried 

 in the tissue of the under surface, the last larval skin being close by adhering to the 

 needle. On tlie 25th the insect had darkened in colour, and had commenced to develop 

 short cottony filaments as follows : — 



(1) At base of head at its junction with the prothorax. 



(2) Two circular patches placed transversely in the sunken depression on prothorax. 



(3) An irregular patch on the meso- and metathorax. 



