ORIGIX AND SIGNIFICAXCE OF SPINES 61 



usually restricted to a kind of special resemblance, and not to 

 the cases of general resemblance afforded by an animal without 

 significant colors in general harmony with its surroundings. 



The influence of mimicry in the production of spines can 

 only occur where the object mimicked is spiniform or spinose. 

 Apparently this is rather infrequent and of little real impor- 

 tance as a factor of acanthogeny. 



Insects and spiders have furnished the greatest number 

 and variety of mimetic forms, both in their larval and adult 

 conditions, and naturally would be expected to furnish ex- 

 amples of spines having mimetic significance. The object 

 mimicked may be another species of insect or animal, in 

 which case there is usually some offensive or defensive 

 quality rendering the resemblance useful to the mimicker; 

 or the whole or a portion of some plant or other object may 

 be imitated, tending to the more or less complete conceal- 

 ment of the mimicking insect. 



Satisfactory examples are not at hand, though doubtless 

 many occur in nature, and some have been described, but not 

 for the present purpose. A few will be cited here which 

 seem to conform to the requirements. 



47 48 



PiGHRE 47. — Profile of a spider {Ccerostris mitralis) on a twig mimicking a 

 spiny excrescence. (From Peckham, after Vinson.) 



Figure 48. — The larva of the Early Thorn Moth (Selenia iUunaria) resting 

 on a twig; showing mimicry of stem and spiniform processes. \. (After 

 Poulton.) 



A Madagascar spider (^Omrostris mitrnlis) is described by 

 Elizabeth G. Peckham ^^ as sitting motionless on a branch 



