294), 'Although the cleft (between the posterior part of the body of the larva 

 of Rumia cratcegata and the branch) is largely filled up, ... a considerable 

 furrow remains, but this is not apparent because of the light color of the 

 fleshy processes, which prevent the attention from being directed to the shadow 

 which would otherwise indicate the position of the groove. The processes, 

 therefore, attain the object of softening the contact between the larva and 

 its food-plant in a two-fold manner, by partially filling up the cleft and by 

 neutralizing the shadow in the groove which remains. I have also noted the 

 processes in the larva of A . betularia, and I believe that they are of very general 

 occurrence in Geometrae.' 



"His other case is to be found in his 'Notes in 1887 upon Lepidopterous 

 Larvae, etc.,' read October 3, 1888. He says (Trans. Ent. Soc. Lond., pp. 

 595-6), 'The most extraordinary thing about this resemblance (of the pupa 

 of Apatura iris to a sallow-leaf) was the leaf -like impression of flatness con- 

 veyed by a pupa which was in reality very far from flat. Thus the length 

 of the pupa was 30.5 mm.; the greatest breadth (dorso- ventral diameter) 

 11. 5 mm.; the greatest thickness (from side to side) 8.5 mm.; . . . But 

 exactly in these places, where the obvious thickness would destroy the re- 

 semblance to a leaf, the whole effect of the roundness is neutralized by the 

 increasing lightness of these parts — a lightness which is so disposed as to 

 just compensate for the shadow by which alone we judge of the roundness of 

 small objects. (Much larger objects can be judged of by the change of 

 focus, which becomes necessary as their near or distant parts are observed.) 

 In shading the drawing of an object so as to represent roundness, the shade 

 is made to become gradually less and less deep as the tangential planes repre- 

 sented come nearer and nearer to a right angle with the axis of vision. So 

 here, the converse of shading— the whiteness neutralizing the shadow which 

 shading is intended to represent — dies off gradually as the (representation of 

 the) mid-rib is approached. 



" 'The whiteness is produced by the relative abundance of white dots and 

 a fine white marking of the surface which is present everywhere, mingled with 



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