56 OF THE FORAMINIFERA GENERALLY: 



types in all other respects, and their dififerences are such as occasionally present themselves 

 to a certain degree between the successively formed portions of one and the same organism, 

 they cannot be generically separated ; and, notwithstanding the extraordinary contrast 

 presented by their extreme forms, both in the shape of their septal plane and in that of their 

 aperture, the one must be regarded as merely a varietal modification of the other. 



69. Since, then, even the characters which in some groups of Foraminifera are most 

 stable, are in others so inconstant as to be quite valueless for the purposes of the systematist, 

 the inquiry naturally arises whether any definite method of generic and specific differentiation 

 can be laid down; and to this inquiry I have to answer — not for myself alone, but for Messrs. 

 Parker and Rupert Jones, whose views on this point are in complete harmony with my own — 

 that in the present state of our knowledge such a methodization is impossible. Whether it will 

 ever be practicable to arrange the multitudinous forms of this group in natural assemblages 

 whose boundaries shall be capable of strict limitation, is to us by no means, certain ; since the 

 tendency of every extension of our researches is to enlarge our idea of the range through which 

 these forms may vary. And all that it seems to us at present feasible to attempt, is to group them 

 around certain generic types, each marked by some combination of characters which impresses 

 on it (so to speak) a distinctive physiognomy, and to trace out the principal modifications to 

 which these types are subject through the separate or combined variation of their characters. 

 Among these modifications there will generally be found some which indicate an afiinity towards 

 other types, so as to diminish the intervals between each type and those to which it is related. 

 Wherever such a gradation can be shown to exist with anything like complete continuity, its 

 presence will be accounted a suSicient reason for including the whole series (however 

 diversified in its extreme forms) under one and the same generic designation ; where, again, it 

 seems likely to be established by further research (which is sometimes especially the case in 

 regard to extinct types), the modification thus related will be ranked as a suh-c/enus ; while the 

 existence of such a decided break between any two types, as enables any specimen at present 

 known to be referred without hesitation (after a sufficient examination of its structure and 

 affinities) to one or to the other, will be held to justify their //ww/e separation. 



70. The impracticability of applying the ordinary method of definition to the (/encra of 

 Foraminifera becomes an absolute impossibility in regard to species. For whether or not 

 there really exist in this group generic assemblages capable of being strictly limited by well- 

 marked boundaries, it may be affirmed with certainty that among the forms of which such 

 assemblages are composed, it is the exception, not the rule, to find one which is so isolated 

 from the rest by any constant and definite peculiarity, as to have the least claim to rank as a 

 nalaral species. Nothing is more easy, however, than to make artijiciaJ species in this group ; 

 for the variation to which every one of its generic forms is liable, gives rise to a multitude of 

 dissimilar forms most inviting to those systematists who consider that credit is to be gained 

 by adding new names to the already enormous list; and accordingly we find that a vast mass 

 of such specific names and definitions has been accumulated, of which but a very few really 

 express the facts they are designed to record. For it is the habit of such systematists 

 to pick out only what they consider the well-characterized types, and to disregard the inter- 

 mediate or osculant forms that establish the gradation between these, neglecting altogether 



