60 ON PLANTS AND INSECTS. [LECT. 



pillars, as for instance that of Ch. porcellus (Fig. 47), 

 have a sort of uncanny, poisonous appearance ; that 

 they suggest a small thick snake or other evil beast, and 

 the so-called "eyes" do much to increase the deception. 

 Moreover, the ring on which they are placed is swollen, 

 and the insect, when in danger, has the habit of re- 

 tracting its head and front segments, which gives it an 



FIG. 47. Chocrocampa porcellus. 



additional resemblance to some small reptile. That 

 small birds are, as a matter of fact, afraid of these cater- 

 pillars (which, however, I need not say, are in reality 

 altogether harmless) "Weismann has proved by actual 

 experiment. He put one of these caterpillars in a tray, 

 in which he was accustomed to place seed for birds. 

 Soon a little flock of sparrows and other small birds 

 assembled to feed as usual. One of them lit on the 

 edge of this tray, and was just going to hop in, when 

 she spied the caterpillar. Immediately she began 

 bobbing her head up and down, but was afraid to go 

 nearer. Another joined her, and then another, until at 

 last there was a little company of ten or twelve birds, 

 all looking on in astonishment, but not one ventured 

 into the tray ; while one bird, which lit in it unsuspect- 

 ingly, beat a hasty retreat in evident alarm as soon as 

 she perceived the caterpillar. After waiting for some 

 time, Weismann removed it, when the birds soon 

 attacked the seeds. Other caterpillars also are probably 



