THE OLDEST NOBLE OF THEM ALL. 



749 



I now come to my oldest noble. It is an established fact that in the 

 most ancient strata in which fossil remains have been found, in the sys- 

 tem called Cambrian, in the primordial fauna, shells occur which differ 

 but little from the living arm-foots of to-day. These older or palaeo- 

 zoic strata fairly swarm with arm-foots ; many rocks are entirely 

 made up of them, and the richness of their forms is inexhaustible. 

 From these earliest ages on, the animal creation gradually assumed 

 more definite shape as the number of individual arm-foots diminished. 

 Doubtless the more perfectly-formed organism superseded the others 

 in the struggle for existence. The noble who relies for the support of 

 his position only on the age of his race-stock, must die out at last if he 

 can not adapt himself by a further development to the demands of the 

 new time. This the arm-foots could not do : they show no progress 

 toward a higher stage of organization. The com- 

 paratively rare brachiopods of our seas are therefore 

 only the scanty relics of departed glory, isolated 

 survivals of a type that was formerly wide-spread 

 and numerous in all the seas. But it is wonderful 

 that a race-shape should have maintained itself 

 quite unchanged through all the geological epochs 

 to our own time ! 



At shallow places in southern seas, there creep 

 a kind of brachiopods in the sand whose shaping is 

 rather like that of a worm than of a brachiopod. 

 It is called the Lingula, or tongue-mussel (Fig. 3.). 

 This creature has an even, somewhat horny shell, 

 and a relatively long and thick stem which is clothed 

 within by a tough layer of muscle. Along with the 

 other species of its kind, it is distinguished from 

 the rest of the family by the shell having no closure, 

 while the bowel, after many turns within the body, 

 opens without. As the valves of the shell only 

 cover the animal, but are not closed tight, they can 

 be easily opened and also moved sidewise upon one 

 another. The animal is never fixed. This is the 

 oldest animal form of the present existing creation. 

 Lingula-shells appear in the Cambrian strata, and 

 have been found in all the geological systems. So 

 far as it is possible to judge from the shells, the 

 genus has propagated itself unchanged through all 

 the earth-history of organisms, has survived all revo- 

 lutions, and has only varied into a few species differ- 

 ing but little from one another. 



In the Silurian strata immediately following these, in which so far 

 nearly two thousand species of arm-foots have been found, are two 

 other still living genera : the one, Discinisca, without closure, but 



Fig. 3. The Lingula. 



