128 HIGH STANDING OF THE PLACOIDS. 



which did not distinguish goats from sheep, nor sheep from 

 cattle. 



The effect of introducing, after this manner, generalizations 

 made altogether irrespective of ranh^ and avowedly without 

 reference to it, into what are inherently and specifically ques- 

 tions of rank, admits of a simple illustration. 



Let us suppose that it was not with the standing of the 

 Silurian placoids that we had to deal, but with that of the 

 mammals of the recent period, including the quadrumana, 

 and even the bimana, and that we had ventured to describe 

 them, in the words of the Edinburgh Reviewer, as " the very 

 highest types of their class." What would be thought of 

 the reasoner who, in challenging the justice of the estimate, 

 would argue that these creatures, men as well as monkeys, 

 belonged simply to that division of red-blooded animals which 

 includes, with the bimana and quadrumana, the frog, the 

 gudgeon, and the earthworm ? — a division, he might add, 

 " which, when details of organization are regarded, stretches 

 farther, both downward and upward," than that division of 

 the white-blooded animals to which the crab, the spider, the 

 cuttle-fish, and the dragon-ily belong ; "so that, looking at 

 one extremity [that occupied by the earthworm], any one is as 

 much entitled to call the red-blooded animals the lowest divi- 

 sion, as any other, looking at another extremity, is to call them 

 the highest division, of animals." "What, ii might well be asked 

 in reply, has the earthworm, with its red blood, to do in a ques- 

 tion respecting the place and standing of the bimana ? Or 

 what, in the parallel case, have the Suctorii — the worms of 

 Linnaeus — to do in a question respecting the place and standing 

 of the real placoids % True it is that, according to one principle 

 of classification, now grown somewhat obsolete, men and earth- 

 worms are equally red-blooded animals ; true it is that, accord- 

 ing to another principle of classification, the placoids of Agas- 

 312 and the cartilaginous worms of Linnaeus are equally Ch(m- 



