ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 



445 



"natural," of the latter of whicli he distinguishes two kinds — dermal, 

 where " the pigment is deposited in the form of very small granules 

 in the cell, or in the product of cells in the cuticula," and hypodermal, 

 where " the pigment is a homogeneous fatty substance, a kind of dye 

 somewhat condensed." Like organic colours in general, the author 

 found dermal as well as hypodermal colours to be subject to the 

 chlorin bleaching processes, which he first applied in 1875, for the 

 purpose of studying the venation of Lepidoptera, the only difference 

 being this, that dermal colours require to be freed, by long macera- 

 tion, from their prison in the chitin. Thus a distinction between 

 dermal and hypodermal colours is that the former bleach only by 

 destruction of the parts in which they are enclosed, the latter bleach 

 readily. The following table is given to serve for the separation, 

 under the Microscope, of the diiferent kinds of coloration. 



'Broken scales become colourless but regain original colora-^ 

 tion if dried again. 



' Washed with alcohol and 

 re-dried, all the un- 

 destroyed scales return 

 to their original color- 

 ation. 



Scales become 

 more trans- 

 parent (if 

 injured) but 

 retain some 

 coloration. 

 Add to the 

 wet scales 

 some chlo- 

 rin-bleach- 

 ing solution 

 and 



/The colour re- 

 mains imtil 

 the scales 

 begin to 

 macerate 

 and lose 

 their struc- 

 tural pecu- 

 liarities. 



1 Optical 



' coloration. 



'Keflected light shows 

 colours complemen- 

 tary to the original 

 coloration. 



Eeiiected light shows ^ 

 same coloration as 

 transmitted light. 



Washing with alcohol and 

 re-drying causes no 

 further change of color- 

 ation. > 



The colour disappears in at most an hour or 

 two, and does not re-appear by any sub- 

 sequent treatment. 



Dermal 

 coloration. 



Hypodermal 

 coloration J 



By this and other modes of separation all the scales of Coleoptera 

 which he had at his command have been studied and only optical and 

 dermal (never hypodermal) coloration was found ; optical coloration 

 being common. In the case of Lepidoptera, optical coloration, except 

 where concealed or subdued by hypodermal coloration, is somewhat 

 rare, and the author never discovered scales where dermal coloration 

 occurred. This may occur in brilliant gold coloured scales, such as 

 some species of Plusia present, but none were at hand to examine. 



An interesting object on which to try this mode of colour-separation 

 is the head of a freshly killed larva of Smerinihus. Upon the ajjplica- 

 tion of strong alcohol, the tubercles lose their milky whiteness from 

 the loss of air, thus proving optical coloration. Chlorin bleaching 

 fluids rapidly destroy the green colour of the fluids of the head, proving 



