334 



ANIMAL DEFENCES 



will serve as an illustration of a spiny covering. The defences of 

 tortoises and turtles have been already described (vol. i, p. 214), 

 but it may be repeated here that such an animal is, as it were, en- 

 closed in a firm box (fig. 492), mostly formed of an upper (carapace) 



and a lower (plastron) shield. 

 Head, tail, and limbs can be 

 more or less drawn back 

 into the shelter thus af- 

 forded. The rear defences 

 are strengthened by an 

 ingenious device in the 

 Hinged Tortoises of Africa. 

 In these creatures the hin- 

 der part of the carapace is 

 connected with the region 

 in front of it by a sort of 

 transverse hinge formed by 

 an elastic ligament, so that 

 when tail and hind-legs are 

 drawn in, the movable part 

 of the shell closes like a 

 spring - door and protects 

 these parts from attack. 

 Armour is singularly deficient in recent Amphibians, but the 

 members of one extinct order of these creatures [Siegocephala) 

 were well off in this respect. A very extraordinary arrangement 

 is found in two living species of newt, i.e. the Spanish Newt 

 {Triton Waltli), and another form {Tylototriton Andersoni) 

 native to the Loo-Choo Islands. These creatures possess long 

 sharp ribs, which sooner or later penetrate the skin. Afterwards, 

 as Gadow remarks (in The Cambridge Nahtral History), " the 

 wounds heal up, the skin forming a neatly -finished -off hole 

 through which the spike projects, not as a formidable, but as a 

 sufficiently awkward, protective weapon". Protection of the kind 

 is well developed in many Fishes. Good examples of firm plates 

 are found in the Bony Pike {Lepidosteus), the Bichir of the Nile 

 {Polypterus), and Coffer-Fishes {Ostracion). Short, strong spines 

 abound on the Thornback Ray {Raia clavata), and the Globe- 

 Fishes {Diodon and Tetrodon) are covered by more numerous 



Fig. 492. — Carapace and Plastron of a Tortoise, from which 

 the external horny plates have been removed 



?j^i-«('8, Neural plates or broadened tops of vertebras; co-cd^, 

 costal or rib plates; lai, nuchal or neck plate; py^, py^, pygidial 

 or tail plates; /?;i-7;:^i, marginal plates; epp, hyop, hypp, xyp, 

 paired plates of plastron; cnp, unpaired plate of plastron. 



and longer defences of the sort. 



In a large number of forms 



