1306 



VARIETIES OF MANKIND. 



variation have been clearly determined in the 

 case of any species which is known to exhibit 

 the tendency, it is obviously impossible to 

 erect specific distinctions that shall possess 

 anything but a provisional value ; and thus 

 the naturalist may feel a confident assurance 

 of the genuineness of one set of species in a 

 natural group, whilst he is utterly at a loss 

 respecting another. 



Reverting, then, to the " idea" of a species, 

 as involving descent from a common, or at any 

 rate from a similar parentage, in all the in- 

 dividuals composing it, we have to aim at 

 ascertaining, in the case of two or more beings 

 whose specific identity or distinctness is a 

 question for our determination, whether their 

 characters are presented so fixedly and deter- 

 minately in all the individuals of the sameand 

 of successive generations, as to justify us in 

 believing that they have been thus preserved 

 through all time, and under all changes of 



~ * ~ 



external conditions. According to the amount 

 and correctness of our information upon this 

 question, will be the validity of our specific 

 distinctions ; on the other hand, according to 

 the hastiness and crudity of our decision, will 

 be its liability to be overthrown by subsequent 

 researches. Of course, where the progeny of 

 any known stock can be traced through a 

 long period of time, and under great varieties 

 of external conditions, and their successive 

 variations have been noted, this evidence must 

 outweigh every argument founded upon the 

 supposed importance of the characters which 

 are found to undergo modification. But such 

 opportunities are too frequently wanting ; and 

 the naturalist is obliged to have recourse to 

 means of discrimination which are less certain, 

 but which will frequently conduct him, pro- 

 vided that his researches have been sufficiently 

 extensive, to a satisfactory conclusion. The 

 great point at which he should aim, is the 

 assemblage of as many forms as possible of 

 each type ; and having done so, he will care- 

 fully compare them with each other, for the 

 sake of determining whether the supposed 

 specific characters are constant and well- 

 marked throughout, or whether they tend to 

 run together by intermediate gradations. If 

 the first of these should prove to be the case, 

 great confidence may be entertained of their 

 genuineness ; but if the second, we may feel 

 an almost certain assurance of their invalidity. 

 Thus, to revert to the case of the apple and 

 the pear, the persistence of their distinctive 

 characters through all the numerous varieties 

 of each, renders it almost certain, that in all 

 other varieties which may hereafter present 

 themselves, the same constancy will obtain; 

 and that it has obtained during the entire suc- 

 cession of generations of pears and apples, 

 from the time of their first propagation. But 

 let us take an opposite case. Two Terebratulce 

 are brought together from different parts of 

 the great Southern Ocean, the one of which 

 has the edges of the valves of the shell thrown 

 into deep plications, whilst in the other they 

 are quite smooth. Now in most other Bivalve 



Mollusca, such a difference would be justly 

 admitted to afford a valid specific character , 

 and the conchologist who had only these 

 two shells before him, would be justified, 

 by the usual rules of the science, in ranking 

 each as a distinct specific type. But as his col- 

 lection extends, intermediate forms come into 

 his possession ; and at last he finds that he 

 can make a continuous series, passing, by the 

 most gradual transition, from the smoothest to 

 the most deeply plicated form. Thus, then, 

 the supposed validity of this distinction is 

 altogether destroyed ; and it becomes evident 

 that the most plicated and the smoothest of 

 these Terebratulce must be regarded as be- 

 longing to one and the same species, notwith- 

 standing the marked diversity of their extreme 

 forms. 



Hence, whilst new types are continually 

 being discovered, the progress of research 

 is tending to diminish the number of species 

 previously enumerated ; for there are many 

 groups in which an immense reduction has 

 been effected, by bringing together all those 

 which are found to be nothing else than suc- 

 cessive stages of the same individual, and by 

 ranking under one designation all those which 

 are either known or strongly suspected to be 

 mere varieties, resulting from the direct influ- 

 ence of external conditions upon themselves 

 or upon their ancestors, or produced through 

 the obscurer operation of these influences on 

 the act of generation. Frequently it is found 

 that forms which have even been accounted 

 genetically distinct, are in reality specifically 

 identical. Thus it has been shown by Pro- 

 fessor Henslow, that the " rust of corn " 

 (Uredo rubigo) is but an earlier form of the 

 " mildew " (JPucdnia graminis) ; the one form 

 being capable of development into the other; 

 and the fructification characteristic of the two 

 supposed genera having been produced from 

 the same individual. And it is asserted by 

 Fries, that out of a single species ofT/ie/eji/iom, 

 more than eight genera of Fungi have been con- 

 structed by various authors. So among higher 

 plants, the invalidity of the generic distinctions 

 on which reliance is usually placed, has been 

 shown, so far as the Orchideous tribe is con- 

 cerned, by the fact that the same individual 

 has borne the flowers and pseudo-bulbs usually 

 accounted characteristic of three distinct 

 genera, and that another individual has pre- 

 sented the character of a fourth.* So in the 

 animal kingdom, it has been shown by Pro- 

 fessor Milne Edwards, that the polypidom of 

 Tubvlipora rerntcosa, according to the circum- 

 stances under which it grows, may present the 

 characters of three other reputed genera. If it 

 be attached to a plane surface, as the expanded 

 lamina of a sea-weed, it remains circular, and 



* For the first of these cases, see the Linn.-ean 

 Transactions, vol. xvii. The second fell under the 

 writer's own observation in the Durham Down 

 Nursery, near Bristol; here, also, three different 

 forms, generally considered as generically distinct 

 were presented ; and two of them were the same as 

 in the preceding case : but the third was one not 

 exhibited by that plant. 



