63 THE CHAIN OF LIFE. 



Brachiopodist labours under the difficulties of not being able to 

 determine wiiat are the simplest, or which are the highest 

 families into which either oi the two great groups of his 

 favourite class is divided ; so far, then, he is unable to point out 

 any evidence favouring progressive development in it. ]iut, 

 confining himself to species, he sees often before him great 

 varietal changes, so much so as to make it difficult for him to 

 define the species; and it leads him to the belief that such 

 groups were not of independent origin, as was universally 

 thought before Darwin published his great work on the Origin 

 of Species. But in this respect the Brachiopoda reveal nothing 

 more than other groups of the organic kingdoms. 



Tv. , (lu.—J'rodiictus cora {M'Orh'xgwy). Carboniferous. 



•' Now, although certain genera, such Si^Terebratnla, Rhynchoti. 

 ellaj Crania, and Discina, have enjoyed a very considerable 

 geological existence, there are genera, such as Strimji^ocephalus, 

 Uncites, Porambonites, Koninckina, and several others, which 

 made their appearance very s'uddenly and without any warning ; 

 after a while they disappeared in a similar abrupt manner, 

 having enjoyed a comparatively short existence. They are all 

 possessed of such marked and distinctive internal characters 

 that we cannot trace between them and associated or synchron- 

 ous genera any evidence of their being eitlier modifications of 

 one or the other, or of being the result of descent with modifi- 

 cation, 'i'herefcre, although far from denying the possibility 

 or probwibility of the correctness of the Darwinian theory, f 



