228 THE COLOURATION OF INSECTS 



These dififerences are sufficiently obvious in the dead 

 specimens, and the quick nervous movements of a live 

 ant with waving antennae are as different as possible 

 from those of a typical spider. 



Nevertheless in this case the spider completely deceived 

 me. How was it done ? Firstly, the shape is unusual 

 for a spider, the cephalo-thorax and abdomen being thin 

 and prolonged, and a constriction in the cephalo-thorax 

 of the spider represents the division between head and 

 thorax of the ant. The spider did not use the first pair 

 of legs for walking, but they were held up in the air and 

 waved about to copy the movements of the antennae 

 of the model. It is obvious that this functional modi- 

 fication necessitates a profound alteration in the neuro- 

 muscular system of the spider. It is worth noting, too, 

 how in the last extremity the spider disclosed its true 

 nature in its endeavours to escape by jumping, a habit 

 common to the family to which it belongs (Salticidae), 

 but suppressed by the new mimetic instinct until an 

 emergency arose. This spider wa? not the only mimic 

 of ^cophylla, for running among them, and almost as 

 closely resembling them as did the spider, was a small 

 bug of the family Capsidae} which proved to be not only 

 an undescribed species, but sufficiently distinct to be 

 placed in a new genus. 



It is of course easier for a bug than a spider to be brought 

 to resemble an ant, since both are insects, and natural 

 selection has the same basis to work upon. It might 

 be supposed that the wings and wing covers of the mimic 

 would prove a difficulty, since they lie over the abdomen, 

 but in Xenetomorpha there is a constriction near the 

 base of the wing covers which, seen from above, matches 

 the constriction between thorax and abdomen of the 

 ant. The bug lives among its models, probably sucking 

 the juices from the stems of the leaves among which 



1 Xenetomorpha carpenter i. 



