1890.J 279 



in the softer parts of the wood. This is a deep cavity, apparently 

 smaller at its mouth than it is beneath, so that the insect is almost 

 completely enclosed. Again, Coelostoma assimile, a New Zealand spe- 

 cies lately discovered, excavates for itself a deep cavity, sometimes in 

 the axils, sometimes in other parts, of the twigs of Fagus Menziesii, 

 and this cavity certainly, I think, extends frequently into th^ wood. 

 Its mouth is covered with a thick waxy mass, and the insect is entirely 

 enclosed. Again, the insect mentioned above as found in Australia on 

 Casuarina combines the process of excavation with the formation of a 

 special covering or shell ; for, keeping the base of its cone always bare, 

 and its rostrum applied to the wood, it covers itself with a horny, 

 tubular test, and afterwards with (inside the tube) a waxy indusium, 

 at the same time sinking deep under the bark, so that at last only the 

 upper portion of the tube is seen to protrude. 



It must be specially noted here that, in all these last three cases, 

 the feet can have but very little to do with the excavation. Gtenochiton 

 viridis and Rhizococcus fossor preserve their feet until the end of their 

 lives, although not using them for locomotion after their earlier stages ; 

 but XyJococcus filiferus in its adult state is entirely apodal, and in its 

 second stage has only very small, atrophied, feet. Coelostoma assimile 

 loses its feet immediately on quitting the larval stage ; and so also, I 

 think, does the new insect on Casuarina. Now, the larva of each of 

 these may, and probably does, begin the burrowing process, but it 

 certainly does not excavate anything like a cavity large enough for the 

 subsequent stages. Clearly, therefore, the feet cannot, in these species, 

 be used to mechanically enlarge the cavities. 



It might be thought that, after all, the excavations are merely due 

 to the increasing growth of the insect, which passively, as it were, 

 prevents the growth of the plant from filling up its usual form. But 

 this, I think, is scarcely the case ; for the depressions and cavities are 

 made not only in the young, soft, immature leaves or tw igs, but also 

 in the harder and older ones. Thus, for example, a larva of Ctenochiton 

 viridis may settle on an old, thick leaf of Coprosma or Panax, and as 

 it undergoes its metamorphoses and reaches the stage of gestation the 

 depression in the leaf begins, grows and deepens. So also the burrows 

 of Coelostoma are to be found in old, as well as in young, twigs ; and I 

 have seen specimens of the Casuarina insect, certainly not adult, in 

 branches more than an inch thick and quite old. I take it, therefore, 

 that the action of the Coccid is not merely one of passive obstruction, 

 but one of active excavation. 



Dr. Low, iu his paper cited above, seems to have tried to make 



BB 2 



