CHAP. xxn. WIDE RANGE OF 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, they 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, consti 

 tuting in the aggregate a single species, one, and indivisible, 

 and capable of being readily distinguished from every other 

 group at present kno^n, 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 transition, the 

 more nugatory does the argument derived from it appear. 

 It then simply resolves itself into one of those exceptional 

 instances of what is called a protean form. 1 



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

 able naturalist, told me that there was 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 mollusca ; for, in proportion as the work was executed 

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

 reputed species pronounced to be a mere variety becoming 

 from that time unsaleable. Fortunately, so much progress 

 has since been made in England in estimating the true ends 

 and aims of science, that specimens indicating a passage 

 between forms usually separated by wide gaps, whether in 



