82 BRITISH LEPEDOPTEKA. 



of the pupa may be a product of the metabolism of the hfemolyrnph that 

 is removed from the fluids of the body by the Malpighian tubules. " 



It is important to notice that Mayer's proof that the scales are 

 formed from modified hypodermic cells makes them truly homologous 

 with the hairs of Arthropods. 



Another important fact insisted on by Mayer is that " the pupal 

 wings exhibit two sets of corrugations or foldings, one being parallel 

 to the trend of the nervures, and the other at right angles to it. In 

 either cross or longitudinal section these corrugations appear as a regular 

 series of ridges, and a single scale arisss from the crest of each ridge." 

 He further writes : "Very large scales are found along the nervures 

 and upon the outer edges of the wings in A. archippus. In fact, these 

 scales are so large, that, after the protoplasm has withdrawn from 

 them, a single leucocyte enters each one. These leucocytes degenerate 

 and finally disintegrate, without, however, contributing directly to the 

 pigmentation of the scale. The fact that the leucocytes degenerate 

 after entering the scales, indicates that the hasmolymph within the scale 

 is not in a normal condition." 



Yet another point insisted upon by Mayer is that " dull ochre- 

 yellow and drabs are, phylogenetically speaking, the oldest pigment 

 colours in the Lepidoptera, for these are the colours that are assumed by 

 the hasniolymph upon mere exposure to the air. . . . Dull ochre- 

 yellows and drabs are at the present day the prevalent colours among 

 the less differentiated nocturnal moths. The diurnal Lepidoptera have 

 almost a monopoly of the brilliant colorations, but even in these 

 diurnal forms one finds that dull yellow or drab colours are still quite 

 common upon those parts of their wings that are hidden from view." 



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 scale pigments. 

 They would appear to consist of the nitrogenous material left in the 

 blood after the building-up of the essential tissues of the insect, formed 

 into definite secretions, which the insect is able to get rid of in a pur- 

 poseful manner in the form of pigments. 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 new material can be obtained, and 

 that only water and C0 2 can escape from the animal, there being no 

 external outlets in the pupa for getting rid of the used-up material, 

 although the urea and urates can accumulate in the urinary tubules. 

 The new combination of the chemical elements which form the tissues of 

 the imago, must, therefore, balance to a nicety that which existed in the. 

 very different structures of the newly-formed pupa (less that which is 

 utilised in producing the change). It is well-known that almost all 

 newly-emerged lepidopterous imagines void one or more drops of fluid 

 with an uric base after emergence from the pupa. This must repre- 

 sent the material which has been utilised by the vital functions accom- 

 panying the processes of histolysis and histogenesis, and that has 

 afforded the necessary force for the formation of the new tissue. 

 Hopkins, Griffiths and others have demonstrated that the pigments of 

 Lepidoptera are derivatives of uric acid, that these uric pigments must 

 arise as the result of the vital activities of the pupa during the time 

 that the imago is being developed, is, we consider, beyond question. 



