6 HISTORICAL SUMMARY. 



can only be based on the careful study of its own plan of organization and of the modifica- 

 tions wliich this shows itself disposed to undergo ; and cannot be safely deduced by analogy 

 from the study of any other group, however closely related. Least of all can any analogy 

 be truly available, which is drawn from one of the highest groups of Invertebrate animals, 

 and applied to one of the very simplest types of animal structure. Had the inquiries of 

 M. D'Orbigny been conducted on a more philosophic method, he must have necessarily been 

 led to the discovery, by the mere comparison of sufficient numbers of individuals, that this 

 analogy is altogether fallacious, and that the ranjje of variation among Foraminifera is so 

 much greater than it is in any of the higher tribes of animals, as to render of no account 

 among the former such differences as in the latter would be of even primary value. But his 

 practice having been (as I have good authority for stating, and as clearly appears also from 

 his results) to select, or to cause to be selected, out of any large assemblage of Foraminifera 

 only the strongly differentiated types, and to leave the intermediate forms altogether out of 

 view, his dominant misconception was not likely to undergo any modification in the course of 

 his researches, and we find it still clinging to him even after he had been satisfied that the 

 true place of this group is among the lowest instead of the highest of the Invertebrate series. 

 Hence it follows that, notwithstanding the immense value and extent of M. D'Oibigny's 

 contributions to this department of Zoology, — in the first place by having brought together the 

 scattered components of the group of Foraminifera, and so differentiated it that it thenceforth 

 took rank as a special object of zoological and physiological study ; secondly, by having 

 brought together from all quarters of the globe and from geological deposits of various 

 periods a vast number of forms previously unknown ; thirdly, by having so far investigated 

 their characters as to be enabled to group them in generic assemblages, of which a con- 

 siderable proportion are tolerably natural ; and fourthly, by having furnished a classification 

 which, although eminently artificial, is still preferable to the chaotic confusion in which they 

 would have otherwise been left, and which has answered a useful purpose as a provisional 

 arrangement, — there is scarcely any part of his work which is likely to stand the test of time 

 and further research. For, as will hereafter appear, a large proportion of his species cannot 

 be legitimately ranked higher tlian varieties, and many even of his genera must be brought 

 down to the same level; whilst the basis of his primary and secondary subdivisions of the 

 group is so unnatural, that it separates under distinct orders not a few types vihich have the 

 closest mutual affinity, and brings into near approximation others which ought to be no less 

 widely differentiated. It will be sufficient here to remark that it is now clearly established 

 that the very same type may develope itself either as a Slichodigue, along a straight or slightly 

 curved axis, or as a Ilelicoste^ue, along a spiral axis; and that certain of the Cydostegue 

 order are generically, if not specifically, identical with certain Helicostegues. Some suspicion, 

 indeed, of the unsoundness of his fundamental assumption that the geometrical plan of hicrease 

 is a character of primary value, appears to have crossed the mind of M. D'Orbigny ; for he 

 admits (lxxiii, p. 17) that affinities exist among all the orders, which arise out of a change 

 in the plan of growth that is liable to occur in many types with the advance of life. This 

 change he affirms (quite erroneously, as we shall hereafter see) to be always in the direction 

 of simplification ; — the more complicated or special mode of increase peculiar to the order 

 giving place to one of a more general character, as where in a Helicosieyuc the spiral extends 

 itself as a straight line, or in an Enallostegue the alternating arrangement of the segments 

 gives place to a uniserial direction of increase. 



