96 THE POPULAR SCIENCE MONTHLY, 



organic condition not disjjlayed in all the vast field of life we have so 

 far reviewed, except imperfectly, in the Cephalopod mollusks. 



This is, at first, attained by the indui'ating of a dorsal layer of 

 flesh into a cartilaginous cord, which stiffens the body while leaving 

 it flexible, and furnishes points for muscular attachment. 



Only a few instances remain of this earlier condition of the Verte- 

 brate type. All others have disappeared. In the embryo of a Tuni- 

 cate animal, the Ascidia, both the cartilaginous cord and the intestinal 

 branchiae appear. In its mature form it becomes a fixed animal, and 

 loses this cord. But in the Ai^pendicularia, a related animal, the cord 

 is retained throughout life. It is also retained, in a more complete 

 develoiDment, in the Lancelet Amphioxus, a creature having strong 

 vertebrate affinities in its extended nerve-cord and its general func- 

 tional system. 



But one further step is required to produce the typical Vertebrate 

 from such an original. This is the formation of joints in the cartilagi- 

 nous cord, when it has become so firm as to resist the lateral move- 

 ments of the body, or is hardened by deposition of carbonate of lime. 



There is nothing in this like the welding of segments in the Articu- 

 late. The vertebrate joints display none of the separate vital animal 

 functions. They yield every indication of being produced in the mode 

 indicated, by the stress of an undulating body. The joints in the sub- 

 sequent limbs resemble them in character, and seem to be formed in 

 the same manner. The Lancelet is not jointed ; it is a single indi- 

 vidual. But the worm from which the Articulate arises is jointed, 

 and each joint is possessed of all the vital functions. 



Thus it appears that the Vertebrate animal starts in the race of 

 life with advantages possessed by none of its competitors. It remains 

 to trace the steps of its develoi^ment. 



THE PEOFUSIOK OF LIFE.* 



By ARABELLA B. BUCKLEY. 



I "WONDER whether it ever occurs to most people to consider how 

 brimful our world is of life, and what a different place it would 

 be if no living thing had ever been upon it ? From the time we are 

 born till we die, there is scarcely a waking moment of our lives in 

 which our eyes do not rest either upon some living thing or upon 

 things which have once been alive. Even in our rooms, the wood of 

 our furniture and our doors could never have been if life did not exist ; 

 the paper on our walls, the carpet on our floors, the clothes on our 

 back, the cloth upon the table, are all made of materials which life has 



* From the Introduction to " Life and her Children," in press by D. Appleton & Co. 



