156 Dynamic TJieory. 



has four limbs, and two large eyes. Its ears are covered under the 

 skin, or wanting. But notwithstanding its apparent external anatomical 

 symmetry tne effects of a want of correlation are apparent in its func- 

 tions. The two sides of the animal seem to be, to a great extent, inde- 

 pendent of each other. One side may be asleep when the other is 

 awake. One eye may look in one direction and the other in another at 

 the same time. The tongue is single and exceedingly quick, the only 

 quick organ it has, for the limbs are exceedingly slow, and ' < unlike 

 most other animals, the Chameleon is totally unable to swim, from the 

 incapabilit} 7 of its limbs of acting in due concert" (Cuvier). The 

 large, single lung appears to relate chiefly to the active, single tongue, 

 and the activity of the animal is chiefly median instead of bilateral. 



Mention is made elsewhere of the case of a female Deer possessing a 

 single horn in correlation with an aborted ovary. The case illustrates 

 the degree of independence which may exist between the two sides of 

 the bilateral body, and also the fact of the individuality and self suffi- 

 ciency of one side by itself. This is also illustrated, and better, by the 

 fact that among birds generally, although the female has two ovaries 

 with oviducts, only one of each is developed into a useful organ, one 

 ovary and one oviduct being reduced to mere rudiments. Same is true 

 of the Ornithorhynchus, as shown above, Fig. 79. 



CHAPTER XXII. 



OSSEOUS SYSTEM. 



The mechanical strains put upon an animal body when it is made to 

 move, are of two kinds, tension strains and compression strains, or 

 strains of pulling and strains of pushing. The simplest spec of proto- 

 plasmic life that moves is under obligation to this mechanical law or 

 necessity equally with the most elaborate vertebrate animal. The parts 

 of the body upon which each of these two classes of strains falls is de- 

 termined by the direction from which it is assailed by the external stim- 

 ulus. Whenever a muscle is stimulated it contracts lengthwise, pulling 

 the ends together. This is a tension strain. When the muscles on the 

 right side of a fish are irritated they contract and shorten that side, 

 causing the head and tail to approach each other, and giving a concave 

 shape to that side. An irritation on the left produces a converse effect. 

 But notwithstanding alternate vigorous pulls of the head toward the 

 tail, the fish is not shortened because these tension strains are thrown 

 primarily upon the backbone, a rigid strut that cannot be compressed 

 longitudinally. So the energy of the tension strain is transferred to 

 motion in the direction of the least resistance ; viz. , a deflection of the 



