An Instance of Mutation. 141 



to me that the ovovivipary of viridis is an advanced stage 

 transitional from oviparv. With regard to the loop the 

 presence or absence of it is by itself an unimportant dis- 

 tinction as it is only the appearance of the Malpighian 

 tubes which will be visible or invisible according as the 

 chit in is thin and transparent or thick and opaque. The 

 variations in P. psidii are so great that those of C. viridis 

 come within their limits. A similar remark holds good in 

 regard to size. The difference in the shape of the dermal 

 cells is not great. There are specimens of C. viridis in 

 which the dermal cells distinctly approach the shape and 

 arrangement in P. psidii (PI. V, fig. 1). The main dis- 

 tinction on which Green appears to rely is. that P. psidii 

 secretes meal and viridis does not. But this distinction 

 breaks down, for in L. Jiemis'phaericum, as I have found, 

 and as Green himself has observed, there is a secretion of 

 meal along the margin. Green says in regard to it that 

 " at this time (of gestation) the inner marginal surface is 

 dusted with white mealy powder, and where a scale has 

 been detached from the plant, an oval white ring marks 

 the previous position." As a matter of fact the secretion 

 of meal is in much greater quantity than indicated in this 

 description, in specimens of L. hemisjphaericum from 

 Mysore (PI. VIII, tig. 1). 



There is also the fact that one apparently healthy mealy 

 bug has been discovered by me to lay eggs beneath the body 

 without a preliminary secretion of meal. Diseased speci- 

 mens have also been occasionally observed to lay eggs 

 without secreting meal. Furthermore, in green bug there 

 appears to be a secretion of meal, though in the minutest 

 quantity. When specimens are lifted off from the leaf 

 they do not always drop to the ground but often hang 

 by a thread, which must therefore be secreted by the bug 

 itself,* and Green notices the presence of wax-secreting 

 glands round the reproductive opening. The resemblance 

 goes further. I have already remarked on the feature of 

 psidii of being tilted at an angle to the surface of the host 

 by the secretion of meal beneath. This habit has been 

 found in large numbers of green bug.f In other species 



* I think that the author has misinterpreted this phenomenon. 

 When one of the insects is detached without unnecessary violence, 

 it will often remain hanging by its long rostral filaments, which are 

 inserted into the tissues of the plant. — E. E. (\. 



f The "tilting"' of the body, in L. viride, is usually a symptom 



