CHAP. XXII. WIDE RANGE OE VARIATION. 429 



above mentioned, must be reckoned by millions of years. 

 According to Mr. Darwin's views, it is only by having at our 

 command the records of such enormous periods, that we can 

 expect to be able to point out the gradations which unite 

 very distinct specific forms. But the advocate of transmu- 

 tation must not be disappointed if, when he has succeeded in 

 obtaining some of the proofs which he was challenged to pro- 

 duce, thc}^ make no impression on the mind of his opponent. 

 All that will be conceded is that specific variation in the 

 Brachiopoda, at least, has a wider range than was formerly 

 suspected. So long as several allied species were brought 

 nearer and nearer to each other, considerable uneasiness 

 might have been felt as to the reality of species in general, 

 but when fifteen or more are once fairly merged in one group, 

 constituting in the aggregate a single species, one and indi- 

 visible, and capable of being readily distinguished from every 

 other group at present known, all misgivings are at an end. 

 Implicit trust in the immutability of species is then restored, 

 and the more insensible the shades from one extreme to the 

 other, in a word, the more complete the evidence of transi- 

 tion, the more nugatory docs the argument derived from it 

 appear. It then simply resolves itself into one of those ex- 

 ceptional instances of what is called a protean form. 



Thirty years ago, a great London dealer in shells, himself 

 an able naturalist, told me that there Avas nothing he had so 

 much reason to dread, as tending to depreciate his stock in 

 trade, as the appearance of a good monograph on some large 

 genus of moUusca; for, in proportion as the w^ork was exe- 

 cuted in a philosophical spirit, it was sure to injure him, every 

 reputed species pronounced to be a mere variety becoming 

 from that time unsalable. Fortunately, so much progress 

 has since been made in Eno-land in estimatino- the true ends 

 and aims of science, that specimens indicating a passage 

 between forms usually separated by wide gaps, whether in 



