Maskell. — On Coccididae. 33 



the plant-growth." In fact, when it is considered how en- 

 tirely devoid Coccids of all genera are of any organs for piercing 

 or cutting, except the rostral suckers, it is difficult to under- 

 stand how they manage to burrow into plants. Here in New 

 Zealand we have such species as Ctenocliiton viridis, which 

 does not indeed form a deep cavit}-, but produces a decided 

 and conspicuous depression beneath its body in the leaf it 

 lives on. Bhizococcus fossor forms a pecuHarly deep pit in its 

 leaf, pressing out the opposite surface in a distinct swelling, 

 and at last almost disappears sometimes in the pit. Colostoma 

 assimile burrows a deep hole through the bark of the tree, and 

 even into the wood, fashioning for itself a complete Httle cavern. 

 How is all this done? In the case of Ctenochifon and Bhizo- 

 coccus, Hving as they do on soft leaves, one might imagine 

 that they use their feet and claws to press out the plant-cells 

 and make the cavities ; but Calostovia assiviile loses its feet 

 almost in its infancy, and the explanation would therefore 

 not suffice in this case. I do not think, moreover, that any 

 mechanical action would altogether accoimt for the pheno- 

 menon : for in specimens of leaves and (as far as I could) of 

 wood examined I do not see any traces of such pressure on 

 the cells as would render them misshapen. Whatever may 

 be the real action of the Coccid, it seems to me that it must be 

 at the same time mechanical and chemical. There must be 

 some chemical reason why certain species form on plants 

 large galls, which are exactly the opposite of cavities ; and in 

 the same way some chemical action must, I think, be exerted 

 to produce the cavities and depressions. But I can offer no 

 plausible explanation myself; and I do not forget that, as fai- 

 as is known at present, Coccids do not exude any acrid or 

 acid fluid likely to exeil active influence on plant-cells. 



It may be observed that pm-ely •• passive" pressure would 

 not sufficiently account for the phenomenon — that is, I do not 

 think that the cavities can be produced merely by the insect 

 lying motionless on the bark or leaf, and permitting the plant- 

 cells to grow round and over it. Such a proceeding would 

 necessarily, I take it, induce some kind of distortion ; but I 

 see no signs of this in the cases referred to. Moreover, in the 

 case of C. assimile and B. fossor, passive obstruction (as it 

 might be called) is not at aiU stifficient to produce in so short 

 a time the deep pits observed. Further, such insects as 

 Lecanium hesperidum, Mytilaspis poyrionan, and scores of 

 others, are just as closely attached to plants as any others, and 

 yet produce no cavities in either leaves or bark, or evei 

 rerv soft substance of fruit. 



