The Colouration of Insects. 81 



Finally, to take the case of caterpillars, Weismann has admirably 

 worked out the life history of many forms, and shows how the 

 complex markings have arisen by development. Broadly, a cater- 

 pillar consists of 13 segments, the head being one. The head is 

 often marked with darker colour, and the last segment with its 

 clasping feet is also very frequently emphasized, as in Figs. 1 & 3, 

 Plate VII. The spiracles are generally marked by a series of spots, 

 and often connected by a line. Here the tendency to repetition 

 shows itself strongly, for not only the spiracles themselves, but the 

 corresponding points in the segments without spiracles are frequently 

 spotted, and, moreover, these spots are frequently repeated in rows 

 above the spiracular line. Of this, Deilephila galii and D. JEuphorbice, 

 Figs. 1-5, Plate VII., are good examples. 



The segmentation is also generally emphasized, as shown in all 

 the examples on the plate, but in its simplicity in Fig. 10. 



Running down the centre of the back a more or less distinct 

 line is often seen, as shown in the figures. This corresponds with 

 the great dorsal alimentary canal lying just below the skin, and 

 Weismann has shown that in young larvae this line is transparent, 

 and the green food can be seen through the skin. We have here, 

 perhaps, a relic of the direct colouration noticed in the transparent 

 coelenterata. 



Where larvae possess horns either upon the head, as in Apatura 

 iris and Papilio machaon, or on the tail, as in many of the sphyngidae, 

 like Figs. 1-5, Plate VII., these appendages are always emphasized 

 in colour. As they are frequently oblique, we often find that this 

 obliquity is continued as a slanting spot, as in D. galii and enphorbice, 

 and sometimes repeated as a series of oblique stripes, as in Fig. 4. 



It must be admitted that in insects we have strong evidence of 

 structural decoration. 



