1893.] Mr. Poulton. Colours of Lepidopterous Larvce. 41 



but are usually of finer texture. As in Myxine, they are developed 

 from the club cells, but there are no special glandular involutions of 

 the epidermis. The club cells of Petromyzon fluviatilis also supply 

 slime threads. 



4. The granular material of the slime is the contents of vesicular 

 spaces developed in the club cells in the immediate neighbourhood of 

 their nuclei, and is set free enclosed in a lattice work developed by 

 vacuolation of the surrounding material, and finally extruded, carry- 

 ing with it the original nucleus of the club cell. 



5. The remainder of the club cell, after extrusion of its vesicle and 

 nucleus, becomes a spirally coiled fibre, which finally breaks up into 

 the fine fibrils of the slime, 



6. Severe stimulation, especially by the vapour of chloroform 

 applied to the intact animal, causes so sudden a development of the 

 coiled fibres from the club cells that the surface of the epidermis is 

 thrown off: and the secretory products set free en masse. This process 

 is of reflex nature, for similar excitation applied to excised skin ia 

 without effect. 



7. A system of connective tissue cells, distinct from chromatophores 

 exists in the epidermis developed from cells which are direct descen- 

 dants of leucocytes, and which can be traced from the blood vessels of 

 the corium through the basement membrane into the epidermis. The- 

 number of these wandering cells in the epidermis is greatly increased 

 by stimulation, probably with a view to providing subsequent 

 support to the secretory elements during regeneration. 



IV. "The Experimental Proof that the Colours of certain 

 Lepidopterous Larvse are largely due to modified Plant 

 Pigments, derived from Food." By E. B. POULTON, F.R.S. 

 Received May 12, 1893. 



(Abstract.) 



The object of this investigation was to afford a conclusive test as- 

 to the theory, previously submitted by the author, that some of the 

 colours of certain Lepidopterous larvae are made up of modified 

 chlorophyll derived from the food-plant. 



Larv83 from one batch of eggs laid by a female Tryphcena pronuba 

 were divided into three lots fed (in darkness) respectively throughout 

 their whole life upon (1) green leaves, (2) yellow etiolated leaves, 

 and (3) white mid-ribs of cabbage. The larvse fed upon (1) and (2) 

 became green or brown as in nature, thus proving that etiolin, 

 no less than chlorophyll, can form the basis of the larval ground- 

 colour. Those fed upon (3), in which neither chlorophyll nor efciolin 



