THE VERTEBRATES 133 



tochord is the precursor of the backbone, and is found 

 at some stage in the development of every vertebrate. 



The amphioxus is a little animal, somewhat fishlike 

 in form, about 2i to 3 inches long, found along the 

 Atlantic coast of the United States. 



When studying the grasshopper, we found that the 

 skeleton was chitinous and wholly external. In the 

 vertebrates the skeleton is wholly internal, except, in 

 some degree, in the turtle. The body of the grass- 

 hopper is segmented throughout, but there is no 

 indication of such segmentation in the body of the 

 vertebrate, except in the vertebrae of the spinal 

 column, and it is probable that this segmentation is 

 not at all homologous to the segmentation of the skele- 

 ton of the grasshopper. 



We found reason to believe that the jaws of the 

 grasshopper move sideways, because they are homolo- 

 gous to legs. No such homology can be traced 

 between the jaws of a vertebrate and the legs of a ver- 

 tebrate. 



No vertebrate has more than two pairs of appen- 

 dages. A centaur, with the body of a horse, and the 

 head, shoulders, and arms of a man, is, of course, 

 a monstrosity. But the monstrous character goes 

 deeper than at first sight appears. An animal like 

 the centaur would necessarily have two hearts, two 

 sets of lungs, two diaphragms, and two sets of ribs. 



It is well for us to consider the relative excellence 

 of the breathing apparatus of the grasshopper and the 

 rabbit. The grasshopper breathes through several 

 spiracles along the sides of the body, and the air is 

 carried in the air tubes throughout the body to the 

 very place where it is to be used. Thus is obviated 

 all necessity for blood as a carrier of oxygen. In the 

 rabbit, the air is taken into the lungs, to which place 

 the blood is also brought, carrying its load of CO2 

 and exchanging it for oxygen. The oxygen is thus 



