606 PROF. E. B. POULTON : NATITEAL SELECTION 



TenthredinidcB, in which the fosterior part of the body is raised on 

 disturbance, while the orange ventral glands are everted and rendered 

 conspicuous. The larva; of Endromis afford a good example of mimetic 

 resemblance almost entirely brought about by appropriate instincts 

 Cthe gregarious instinct, the movements and attitudes assumed on 

 disturbance). Thus the results are due to internal changes (in the 

 nervous system) with only a minimum of superficial modification. 

 Fig. 3. Natural size. A group of larger larvae of Endromis versicolor, also 

 drawn upon birch by P. J. Bayzand. The figure shows that as the 

 larvffi increase in size their instincts undergo appropriate changes 

 leading them to form much smaller gi-oups like the smaller groups of 

 the more advanced larviB of TenthredinidcB. The attitude represented 

 is that which follows disturbance. 



Figs. 4-9 were drawn from specimens in the Hope Department, and are intended 

 to show the retention of ancestral features upon parts which are 

 normally concealed and the restriction of mimetic modification of 

 colour and pattern to the parts which can be seen. They incidentally 

 show examples of the more complete development of mimetic resem- 

 blance in the female sex. 

 Fig. 4. About I natural size. The male of Bismorphia praxiiioe, showing the 

 manner in which the long-and-narrow-winged appearance of an 

 Ithomiine is brought about in this broad-hind-winged butterfly. A 

 comparison of the right and left sides of the figure clearly indicates 

 the manner in which this appearance is produced by the excessive 

 amount of overlap which occurs in the natural position of the wings 

 (left side). Hence the greater part of the surface of the upper side of 

 the hind wing and the under side of the fore wing is hidden in a natural 

 position, and upon these concealed parts a large patch of the old 

 Pierine white appearance is retained, seen, in the case of the hind 

 wing, on the right side of the figure. 

 Fig. 5. About I natural size. The male of Bismorphia praxinoe, showing the 

 under side of the wings in the natural position (left side), and with 

 the wings separated on the right side so as to expose that part of the 

 under surface of the fore wing which is normally concealed. Here, 

 too, a large white patch is to be seen. 

 Fig. 6. About I natural size. The female of Bismorphia praxinoe, figured in 

 the same manner ae the male in fig. 4, and showing that the wings are 

 really long and narrow with only the amount of overlap which is 

 usual in butterflies. No white is to be seen upon the narrow band of 

 the hind wing, which is concealed in the normal position. 

 Fig. 7. About I natural size. The female o^ Bismorphia praxinoe, figured to show 

 the under side of the wings similarly to that of the male in fig. 6. 

 Here, too, it is seen that no white patch like that of the male is 

 retained. 

 Fig. 8. About I natural size. The male of Bismorphia orise represented in the 

 same position as that of the male of B. praxinoe in fig. 4. Here, too, 

 in this transparent, black-barred species, immensely modified by 

 mimetic resemblance, the white patch is still retained (in the male), as 



