ADAPTATION 237 



Defensive Weapons, These may be the same as aggressive in 

 vertebrates. The teeth and claws of many herbivorous animals 

 are excellent weapons. They also include structures in no way 

 correlated with securing food. The tail of Stcgosanriis, for ex- 

 ample, with its enormous bony spines, must have been a terrible 

 weapon, and the tails of modern Oocodilia are effective clubs. 

 Horns of ungulates should be mentioned here, although they are 

 also organs of aggression in individual combat within the species. 

 The stings of insects an^ among the most highly developed de- 

 fensive weapons (Fig. 145). 



Glandular Secretions. Some animals are provided with glands 

 which secrete poisonous substances or repulsive scents. Many 

 insects have such glands. The stink-luigs derive their popular 

 name from their unpleasant secretions, and many other true bugs 

 secrete more or less unpleasant substances. The larvae of the 

 common swallow-tail butterflies have an eversible scent organ 

 just behind the head which has been shown to be repulsive to 

 birds. The scent produced by the skunks requires no detailed 

 discussion, nor does the venom of poisonous snakes. 



Electrical Organs. A few animals are able to defend them- 

 selves by discharging electricity from special organs. The electric 

 rays and eels are capable of giving severe shocks. 



Concealing Discharges. Such discharges have already been 

 mentioned under adaptations to deep-sea life. The discharges of 

 Cephalopoda and of the deep-sea prawn are the only familiar ex- 

 amples of this adaptation. 



Autotomy. One of the most striking of all defensive adaptations 

 is autotomy. In some lizards the tail is brightly colored and so 

 is most likely to be the part seized by a carnivorous species, but 

 if grasped it breaks away from the body and the lizard is able to 

 scamper away to raise a new appendage. Crabs are said to drop 

 off claws if seized by them. Such powers are usually correlated 

 with ability to regenerate the lost appendages. The term autot- 

 omy is sometimes a misnomer in this connection since the loss of 

 parts may apparently be due more to fragility of structure than to 

 the animal's power to drop appendages at will, although the latter 

 is sometimes present. The term is also, and more accurately, 

 applied to the process of fission. 



Animal Associations. Gregariousness. Many animals obtain 

 by association with others of the same species or with different 



