362 ANIMAL DEFENCES 



a defensive arrano-ement found among: a number of the higher 

 Protozoa. The outer layer of this creature's body is packed with 

 innumerable rod-like bodies {trie ho cysts), which can be shot out 

 when their owner is irritated, much like the rods in the skin of 

 some Planarian Worms, and the rods would appear to possess 

 irritant properties. It must be remarked, however, that after 

 these structures have been brought into play their possessor dies, 

 breaking up into a number of pieces; so that, as in the case of 

 the Honey-Bee (see p. 358), the arrangement is one by which 

 the species benefits at the expense of the individual. 



Co-operation for Active Defence among Social Animals. 

 — Some of the herbivorous Mammals which live in communities 

 co-operate for defence in a very skilful manner, though, to begin 

 with, retreat is usually the first proceeding, and it is only when 

 obliged to make a stand that they turn upon their enemies. A 

 good instance, that of Wild Horses, has already been quoted 

 (see p. 350), and space prevents further examples from being 

 given in this section. 



