216 LAY SERMONS, ADDRESSES, AND REVIEWS. [x. 



changes as great changes, which from one point of view 

 they truly are. But leaving the negative differences 

 out of consideration, and looking only at the positive 

 data furnished by the fossil world from a broader point 

 of view — from that of the comparative anatomist who 

 has made the study of the greater modifications of 

 animal form his chief business — a surprise of another 

 kind dawns upon the mind ; and under this aspect the 

 smallness of the total change becomes as astonishing as 

 was its greatness under the other. 



There are two hundred known orders of plants ; of 

 these not one is certainly known to exist exclusively 

 in the fossil state, The whole lapse of geological time 

 has as yet yielded not a single new ordinal type of 

 vegetable structure. 1 



The positive change in passing from the recent to the 

 ancient animal world is greater, but still singularly 

 small. No fossil animal is so distinct from those now 

 living as to require to be arranged even in a separate 

 class from those which contain existing forms. It is 

 only when we come to the orders, which may be 

 roughly estimated at about a hundred and thirty, that 

 we meet with fossil animals so distinct from those now 

 living as to require orders for themselves ; and these do 

 not amount, on the most liberal estimate, to more than 

 about 10 per cent, of the whole. 



There is no certainly known extinct order of Protozoa; 

 there is but one among the Coelenterata — that of the 

 rugose corals ; there is none among the Mollusca ; there 

 are three, the Cystidea, Blastoidea, and Edrioasterida, 

 among the Echinoderms ; and two, the Trilobita and 

 Eurypterida, among the Crustacea ; making altogether 

 five for the great sub-kingdom of Annulosa. Among 

 i 



I l See Hooker's " Introductory Essay to the Flora of Tasmania," 



