334 



LEPIDOPTERA 



CHAP. 



articulation of the scale, with the wing takes place by a division 

 of the stalk of the scale where it is encompassed by the mem- 

 brane. Semper was not able to show that the scale-forming 

 cells are certainly hypodermal cells, but this has since been 

 demonstrated by Scha'ffer, who also shows that each of the cells 

 contains an excretory vesicle. 



Very little is positively known as to the development of the 

 colour in the wing-scales. It has been pointed out by Hopkins l 

 that in some cases the colours are of the nature of urates ; that 

 is, of excretory matter of the kind that usually passes from the 

 body by direct channels, and in the case of Lepidoptera, by the 

 Malpighian tubes. Miss Newbigin suggests that the organic 

 pigments used in scale -coloration will be found to be of two 



B 



FIG. 175. Early condition of scales and nervures. (After Semper.) A, Section of 

 portion of wing of pupa of Sphinv pinastri ; a, basal membrane with trachea 

 beneath it ; c, scale-forming cell ; <l, early state of a scale ; e, e, more advanced 

 stages ; /, hypodermal cells. B, part of a cellular cylinder that excretes the 

 nervure [or more probably the rib or " Rippe " of Schiitt'er ; cf. Fig. 170, B] ; b. 

 epithelial [hypodermal] cells ; , central string [supposed by Semper to be a nerve]. 



kinds, urates and melanins, the urates being derivatives from nitro- 

 genous, the melanins from carbonaceous, matters. 2 Marchal, who 

 has devoted a great deal of attention to the study of the Malpi- 

 ghian tubes, informs us that the subdermal pigments of cater- 

 pillars are frequently in large part deposits of urates, and he is 

 of opinion that, the function of the Malpighian tubes being 

 arrested at certain periods of the metamorphosis, elimination of 

 the matter they separate when functionally active then takes 

 place in a variety of other ways. 3 A similar condition as to 

 the melanin-pigments and the respiratory functions appears also 



1 Phil. Trans. 186 B, 1896, No. 15. * Natural Science, viii. 1896, p. 94. 



3 Bull. Soc. ent. France,-1896, p. 257. 



