270 I November, 



perhaps are more valuable or handy than those derivable from the 

 arrangement of the frass. Moreover, they are of especial interest as 

 illustrating the effect of physical conditions on the habits of an insect, 

 for there can scarcely be a doubt that the various forms of frass ar- 

 rangement are governed in the main by the transverse capacity of the 

 mine, as this is determined partly by the breadth of the mine, and 

 partly by the extent to which the parenchyma is removed. 



What we find, therefore, is this. Where the mine is capacious, 

 as it must be in a wide gallery, or even in one only moderately wide, 

 provided the parenchyma has been freely removed, the larva finding 

 abundance of room and the walls of its mine easy of distension, packs 

 its frass behind it, pellet upon pellet, in a narrow continuous track 

 down the middle of the mine. But if its capacity be restricted or the 

 tension of its walls increased, either from want of breadth or from a 

 thick layer of parenchyma left in its floor, the larva can no longer 

 heap pellet upon pellet in the former labour-saving way, but is obliged 

 to turn the end of its body first in this direction and then in that, and 

 seek a vacant spot for each separate grain, so that the frass gets 

 generally distributed over the mine. In the one case a broad free 

 space is left at the sides of the mine, in the other none at all or next 

 to none. Now, these two modes of disposal have long been recognised 

 and turned to good account, but there is a third mode, or rather a 

 form of the last mentioned one, that appears to have escaped notice, 

 and is yet of more than usual interest as illustrating in a high degree 

 the principle which I have suggested is at the bottom of the whole 

 question. It is found in greatest perfection where the mine is either 

 very narrow or very shallow. Under such circumstances space being 

 none too plentiful, economy in its use becomes a necessity, and 

 just as under like conditions in every day life experience teaches us 

 that this can only be accomplished by the employment of order and 

 method, so the larva seems to have learnt the lesson also, and instead 

 of scattering its frass incontinently over the mine deposits the indi- 

 vidual grains with the nicest precision, side by side in slightly curved 

 rows across the mine. Indeed, I do not think it would be possible to 

 take up a mine of continuella, of hasigidtella^ or of distinguenda, stuffed 

 often as full as it can hold, without being struck with the singular 

 beauty of the arrangement, and being at the same time convinced 

 that by no other means could the frass have been successfully packed 

 away. From the resemblance of the superimposed rows to the coils 

 of a spring, I shall speak of it as the " coil arrangement," or of the 

 frass as "coiled." 



