MEANING OF JAGUAR AND LEOPARD ROSETTES 109 



action of the nervous system influences the pigmentation of the 

 skin, and the distribution of the pigments ; but the nerves them- 

 selves seem to act only as conductors of the changes and influences 

 which lie deeper in the cells of the nerve-centres. In electro-plating 

 the wires conduct the influence of the action in the battery, and 

 the metal is separated from the solution, and is deposited on 

 the plate, or is dissolved off again, and returned to the solution 

 according to circumstances. So in the pigmentation of the 

 skin, the influence of the nerve-centres, acting through the 

 nerves, puts on or takes off pigment, and modifies it according to 

 circumstances. 



Now the action of the nerve-centres depends on the blood, and 

 the blood depends on food and physical surroundings. But in 

 addition to all these, heredity undoubtedly plays a great part in all 

 these phenomena. And in order to answer the question I put, we 

 have to go back to features of still more ancient animals, which are 

 now wholly extinct, viz., of that large class of animals which 

 carried armour plates on their skin, as part of what is called an 

 exoskeleton. 



In remote times there were numerous animals protected by 

 plate-armour ; some of these have continued as survivals up to our 

 time such as Armadillos, Turtles, Crocodiles, Sturgeons, and many 

 other curious fishes. Indeed, if we go lower down in the scale of 

 life, we find that the exoskeleton is the only solid part of the 

 animal structure, such as we see it in Crabs, Lobsters, and other 

 A rthropoda. 



Among armour-plated animals, now extinct, were several known 

 species of Glyptodonts, like that shown in Fig. 60, the fossil original 

 of which is in the Natural History Museum. 



The armour of these strange animals consisted of either circular 

 or many-sided plates, encircled by a rim of smaller polygonal 



