36o ANIMAL DEFENCES 



eye. Although the secretion is therefore useful as a defence 

 against vertebrate enemies, it is probably chiefly directed against 

 ichneumons." As regards the latter point, it is known that this 

 larva is very liable to the attacks of a particular species of 

 ichneumon-fly {Faniscus cephalotes), which lays her eggs upon 

 its skin. The larvse which hatch out from these use the unfor- 

 tunate caterpillar as a food-supply. Experiment has shown that 

 the acid secretion is either immediately fatal or else highly in- 

 jurious to ichneumons upon which it happens to tall. 



The hairs which clothe many caterpillars produce a highly 

 irritating effect upon the mouths of insectivorous animals (or 

 the fingers of human beings), and this is pardy the result of their 

 being barbed, besides which they are probably endowed with 

 poisonous properties, like the spines of certain fishes (see p. 355). 

 Such aggressive hairiness is associated with warning-coloration 

 (see p. 301). A typical example is that of the Palmer Worm, 

 which is the larva of the Gold-tail Moth [Port/icsia aurifliid), 

 and is rendered conspicuous by its markings of white spots and 

 red lines upon a black ground. The barbed hairs are not the 

 only disagreeable point about this caterpillar, for it also possesses 

 defence-glands opening on the upper surface of the body, and 

 secreting an acrid fluid. 



Actively Defensive Weapons of jMyriapods and Pcripatiis. — 

 Centipedes would appear to be sufficiently defended by the 

 possession of poison-jaws, primarily weapons of offence. Milli- 

 pedes, however, are non-aggressive vegetarian creatures devoid of 

 such structures, and repel the attacks of their enemies by means 

 of numerous stink-glands, which open on the sides of the body and 

 secrete an offensively-smelling fluid containing prussic acid. 



The slime-glands of Peripatiis, which open on two papillae 

 near the mouth, would appear to be special means of defence, 

 though, in the New Zealand species at any rate, they are also 

 employed in the capture of prey. Speaking of the Cape species 

 Sedgwick says (in The Cambridge Natural History): — " They will 

 turn their heads to any part of the body which is being irritated 

 and violently discharge their slime at the offending object ". 



Actively-Defensive Weapons of Lozuer Invertebrates. — The 

 numerous and often powerful setae with which many of the marine 

 Bristle-Worms are provided would seem, in some instances at 

 least, to serve for active as well as passive defence, though there 



