1600 THE STORY OP THE UNIVERSE 



(though that is not the appropriate word) the ap- 

 pearance of other species is still far from being 

 understood. All we know is that this power, this re- 

 semblance of a beetle or a butterfly to the ground 

 upon which it sits, the sticks among which it creeps, 

 or the leaves among which it flutters, helps to save 

 it from destruction, while it is a decided advantage 

 to it to "mimic" another insect which is sedulously 

 avoided by birds. The observations in this byway 

 of zoology are as curious as any yet made. It 

 is found, for instance, that an American spider 

 (Cyrlarachne) takes the semblance of a little land 

 shell very abundant in the localities which it fre- 

 quents; and that another species (Thomisus alca^ 

 torius), remarkable for the length of its forelegs, 

 so fastens itself on the stems of grasses as to be nearly 

 indistinguishable from the spikelets. 



Some observations, for which we are indebted to 

 M. Heckel of Marseilles, throw a good deal of light 

 on the origin of mimicry, at least so far as the as- 

 sumption of protective coloration is concerned. 

 There is a spider (Thomisus onustus) very common 

 in the south of France which conceals itself in the 

 flower of a species of wild convolvulus for the pur- 

 pose of trapping two kinds of fly on which it feeds. 

 This convolvulus is found in three principal vari- 

 eties: white, pink with deeper spots of the same hue, 

 and light pink forms with a slight greenishness on 

 the external wall of the flower. Each of these three 

 varieties is visited by the spider. But the varieties 

 of spider conform in hue to the varieties of the flower, 

 and each confines itself to the one which is most pro- 



