252 t^pr". 
frequent colouration of the skin by the salts of silver when taken internally, 
and the hue given to the bones of animals by the exhibition of madder. It is 
not unreasonable to suppose that the bright orange of the lichen might remain 
as a pigment unaltered just in a similar way. Experiments might be made 
with the Cleora or BryopMlcB ; or colouring matter, such as madder, might be 
mixed with the food of Aglossa, or with the wax of Galleria, &c. But in 
general, the colouring matter of plants is too fugacious for us to expect a 
change in hue from this cause. I had this year two larvae of Pldogophora 
meticulosa of a bright carmine colour, from feeding on heath blossoms : the 
moths in no way differed from the ordinary examples. 
4. Soil. — The only way in which we can conceive this to act is, that a moist soil 
strongly impregnated with some metallic oxide might, by endosmose, stain the 
tissues in a naked pupa, and so an artificial colouration might be produced. 
5. Retardation or acceleration of development. — Dr. Knaggs has given in the case of 
illustra/ria a most interesting example — the only one, I believe, in which a 
variety can be produced at will. The interest attached to this must be my 
apology for asking him to give still further particulars. It will be seen that 
there is one great difference between the case of E. illustraria and of P. ra/pw. 
In experiments with P. ra^ae the larva has been allowed to feed as usual ; the 
development of the pupa has alone been abridged. In illustra/ria the larva has 
fed up rajjidly as well, and has gone into the pupa stage prepared for a short 
period of quiescence. If Dr. Knaggs has, by heat or other causes, accelerated 
the last stage alone, and still produced the summer form, it would add to the 
interest of the experiment. Yet a variety produced at will is a great achieve- 
ment. 
A great many of the boreal varieties occur, however, in single-brooded 
insects ; — for example, in polyodon, lithoxylea, occulta, festiva. 
The summary of probable causes is here tried to be stated with fairness, and 
it is hoped experiments will be made by those who have the leisure, and the results 
(negative as well as positive) published. 
The writer has himself a strong bias in favour of the action of light ; and it 
must be remembered that, if one larva feeds ujd in twenty-five days and another in 
thirty, the latter has one-sixth more light during its larval stage than the former. 
We have not as yet solved all the mysteries attendant on the retardation or accele- 
ration of development. Heat is, without doubt, a powerful agent ; yet there is 
often a year's difference between the pupae of Eriogaster lanestris, exposed, as far 
we can see, exactly to the same thermal influences. The following extract from a 
Canadian letter may be interesting : — 
"P. rapce was quite plentiful with us last year. The spring and fall 
"broods differ here as they do with you." 
R. C. R. Jordan, Birmingham. 
Notes on variation in Lepidoptera. — At page 236 of the Ent. Mo. Mag., the 
Rev. J. Greene asks how it can be proved that " the lemon-coloured variety (query) 
of Xanthia cerago" is veritably X. cerago. I think that Mr. Greene is quite right 
when he says he believes it has never been bred from eggs laid by an ordinary 
cerago ; i. e., if he thereby mean from oggs laid in confinement by an ordinary 
