XXVI IVAR trad(;ardh. 



miners. The different mode of mining is also reflected in the armament of 

 the cuticle. In all the necessity of increasing the friction against the walls 

 of the mine existed, but as the spruce-needle miners as a rule leave the 

 mines through the same aperture through which they enter, and consequently 

 must be able to move both backwards and forwards, this emergency is met 

 by the semispherical processes of the cuticle, whereas the pine-needle miners, 

 mo\'ing only in one direction, have the cuticle provided with small spines 

 directed backwards. 



Comparison betueeii the pine-needle miners. 



Of these Heringia dodecella only mines when young, hibernating in a needle 

 and attacking the shoots the following spring, while Cedestis, Dyscedestis and 

 Ocnerostoma are exclusively needle miners. In these the last instar differs both 

 in biology and morphology from the other ones, its only function being appa- 

 rently to spin the cocoon for the pupation. The last instar lacks many of 

 the typical mining characteristics possessed by the other instars, such as the 

 yellowish-red colour, the cuticular spines and the well chitinized prothoracic 

 shield, which are adaptations to this peculiar mode of life, the last instar 

 being thus the more primitive and less specialized. As regards the method 

 of mining, Cedestis is the less ingenious, working from the base of the needle 

 towards the top and thus cutting off the afflux of the sap, while the other 

 work towards the base, which enables thera to have fresh food even through 

 the winter. Heringia dodecella mines in the distal part of the needle, which 

 gives it shelter during the winter and food the following spring before it 

 attacks the shoots. 



All these three exclusive pine-needle miners have a very peculiar struc- 

 ture in the hind end of the abdomen, described in Cedestis in a previous 

 paper by the present-writer (I, fig. 9). The dorsal side of the base ofthe anal feet 

 and the ventral side of the suranal lobe are armed with small, dentate scales 

 (fig. 40 b), forming a funnel behind the anal aperture, the walls of which are 

 clothed with dentate scales. In the previous paper, when this structure was 

 only known in Cedestis, the author suggested that its function was to compress 

 and pack together the excrements in the mine in order either to widen the 

 limited space at the disposal of the larva in the mine, or to get the excre- 

 ment dry as soon as possible in order to prevent the growth of fungi. The 

 presence of identically the same structure in the two other pine-needle miners 

 seems to show that this is preeminently a pine-needle miner adaptation. Regard- 

 ing its function, the author is still of opinion that it serves the purpose of 

 packing the pellets closely together, the ability of the larva to compress these 

 being, however, more doubtful. It is true that the pellets are exceedingly 

 small and quite dry, but this may be effected by the action of the hind 

 intestine alone. The packing together of the pellets, on the other hand, can 

 endently only be effected by the action of the hind end of the body, the 

 three lobes with their scales spreading and pushing against the pellets. It 

 is, however, possible that the main significance of this is to enable the larva 

 when feeding to press its head against the vall in front of it, and this it 

 would to all appearance be impossible to accomplish, if the top of the abdomen 

 were shaped otherwise. 



