44 



colour impression we observe. Colours produced in this way we call 

 "pigmentary." 



Mayer's demonstration that the pigmentary matter deposited in the 

 scales of Lepidoptera is a derivative of the blood secreted at a time 

 when the histogenesis of the tissues of the imago has been completed 

 within the pupa, gives a hint as to the actual nature of pigments. 

 They would appear to consist of the nitrogenous material or waste 

 present in the blood left after the building up of the essential tissues 

 of the insect, formed into definite secretions, which the insect is 

 enabled, as pigment, to get rid of in a purposeful manner. It must 

 not be forgotten that all the vital activities of the pupa are taking 

 place in a multitude of ways in a closed cell ; that no waste can be 

 excreted, there being no outlets in the pupa for this purpose ; and 

 therefore the new combination of chemical elements which forms the 

 tissues of the imago must balance to a nicety those that existed in 

 the very different structures of the newly-formed pupa. It is well 

 known that almost all newly emerged lepidopterous imagines void 

 one or more drops of fluid with a uric base after emergence from the 

 pupa. This must be the residue of the material not utilised by the 

 vital functions accompanying the processes of histolysis and histo- 

 genesis. 



Many years ago Meldola demonstrated that the yellow pigment of 

 Gotiepteryx rhamni was soluble in water, and that the aqueous solu- 

 tion had an acid reaction. Krukenborg discovered that in the blood 

 of different beetles and lepidopterous pupre there were various 

 colouring matters constant in different species, and readily recognis- 

 able under the spectroscope, and specially noted the yellow-brown 

 lymph of Attacus pernyi and the yellow-green lymph of Saturnia pyri. 

 Hopkins has shown that the yellow pigment in certain Pierid butter- 

 flies is a derivative of uric acid ; and Griffiths has demonstrated that 

 the green pigment found in several species of Papi/io, Limenitis, as 

 also in various Sphingid, Geometrid, and Noctuid species, also con- 

 sists of a derivative of the same product. This has been termed 

 " lepidopteric " acid. We have already shown how these uric pig- 

 ments must arise as the result of the vital activities of the pupa during 

 the time that the imago is being developed. 



It is impossible, in the time at our disposal, to enter any more 

 fully into this phase of the subject. One thing appears quite cer- 

 tain, however — viz. that the nature of the pigmentary deposit is as 

 characteristic for each individual species as are the shape and struc- 

 ture of the scale in which it may be deposited. With those who 

 consider that the colours of insects originate within the insects them- 

 selves we are inclined to agree, since there can be no doubt that the 

 nature of the pigmentary deposits and the scale-structure determine 

 absolutely the colours of the insect. With those who ascribe the 

 phenomena of colour variation to internal causes we should agree so 

 far— and only so far — that a difference of physique, and consequent 

 available energy, would necessitate a difference in the quality of, or a 



