216 ANIMAL COLOEATIOK. 



There remains, however, in the mimicking genera the re- 

 semblance of colour, which is siiperadded to that of form ; and 

 the colour resemblances in these cases of mimicry are perhaps 

 to be regarded as more striking than those of form. 



In some instances, however, which have been used to 

 illustrate the phenomena termed mimicry, the form resem- 

 blances are as striking as, or even more striking than, the 

 coloiar resemblances. 



Spiders mimicking Ants. 



Mr. E. C. Peckham has recorded several instances of 

 spiders which appear to mimic ants ; these are possibly 

 examples of " aggressive mimicry " ; the imitation enables the 

 spider to approach the ants undetected. It has been suggested, 

 on the other hand, that a more probable explanation is to secure 

 the immunity of the spiders from the attacks of birds which 

 do not prey upon ants. 



But neither of these hypotheses is thoroughly satisfactory. 

 In a conflict between an ant and a spider of about the same 

 size, the fortune of battle would be very uncertain ; this would 

 be no case of a wolf in sheep's clothing. On the other hand, 

 ants are preyed upon by so many different animals — mammals 

 as well as birds — that the advantage of another animal, so to 

 speak, going out of its way to mimic them is at least doubtful. 



The resemblances between the spiders in qirestion {e.(j., 

 Synageles picata and Synemosyna formica) and ants is not 

 limited to shape, but is also shown in colour. In these cases, 

 however, unlike Leptalis and the Helicon idfe, the colour 

 resemblances might well, if it were necessary, be left out of 

 consideration, for a blackish-brown or yellowish-brown is a 

 common hue of Arthrojioda, covered as they are externally with 

 a shell of chitin. Ot^ier causes, therefore, ]ierhaps comparable 



