VERTEBRA OP THE SERPENT. 315 



adjusted to the form of their whole, and to their habits and 

 sphere of life, as is the organization of any animal which we 

 call superior to them. 



" It is true that the serpent has no limbs, yet it can out- 

 climb the monkey, outswim the fish, outleap the Jerboa, and, 

 suddenly loosening the coils of its crouching spiral, it can spring 

 into the air and seize the bird upon the wing : all thesa 

 creature^ have been observed to fall its prey. 



" The serpent has neither hands nor talons, yet it can out- 

 wrestle the athlete, and crush the tiger in the embnice of its 

 ponderous overlapping folds. Instead of licking up its food as 

 it glides along, the serpent uplifts its crushed prey, and presents 

 it, grasped in the death- coil as in hand, to its slimy, gaping 

 mouth. 



" It is truly wonderful to see the work of hands, feet, and 

 fins performed by a modification of the vertebral column 

 by a multiplication of its segments with mobility of its ribs. 

 But the vertebrae are especially modified, as we have seen, to 

 compensate, by the strength of their numerous articulations, 

 for the weakness of their manifold repetition, and the conse- 

 quent elongation of the slender column. 



" As serpents move chiefly on the surface of the earth, their 

 danger is greatest from pressure and blows from above ; all the 

 joints are fashioned accordingly to resist yielding, and su^tiin 

 pressure in a vertical direction ; there is no natural undulation 

 of the body upwards and downwards it is permitted only 

 from side to side. So closely and compactly do the ten pairs 

 of joints between each of the two hundred or three hundred 

 vertebras fit together, that even in the relaxed and dead state 

 the body cannot be twisted except in a series of side coils." 



THE upper right-hand figure represents a portion of the 

 shell of an Echinus, or Sea-urchin, together with two of the 

 spikes. 



The reader will remember that in the description of thfe 

 Heart-urchin, and the mode in which it dug its way into the 

 sand, the peculiar mobility of the spines was mentioned. How 

 that mobility is produced we shall now see. 



If a living Sea-urchin can be procured, and placed in a 

 glass vessel filled with sea -water, it will at once be seen that 



