198 ORIGINAL ARTICLES-. 



thirty varieties, stand really in the place of ancestral representatives of 

 certain existing Foraminifera, that they pnt on their several snbspecific 

 features in accordance with the conditions of their place of growth, just 

 as their posterity now do ; and that although we have in this instance 

 met with only the minute forms of a 700-fathoms mud-bottom, yet else- 

 where the contemporaneous fuller development of these specific types 

 may be found by careful search in other and shallower deposits of the 

 Trias period"*. 



It can scarcely, I think, be questioned that such a continuity of the 

 leading types of Foraminifera maintained through so long a series of 

 geological periods, and the recurrence of similar varietal departures from 

 those types, is a result of the facility with which creatures of such low 

 and indefinite organization adapt themselves to a great variety of exter- 

 nal conditions ; so that, on the one hand, they pass unharmed through 

 changes in those conditions which are fatal to beings of higher struc- 

 ture and more specialized constitution; whilst on the other, they undergo 

 such modifications, under the influence of those changes, as may pro- 

 duce a very wide departure from the original type. 



Thus we have found strong reason for regarding temperature as 

 exerting a most important influence in favouring, not merely increase 

 of size, but specialization of development ; all the most complicated and 

 specialized forms at present known being natives either of tropical or of 

 sub-tropical seas, and many of these being represented in the seas of 

 colder regions by comparatively insignificant examples, which there seems 

 adequate reason for regarding as of the same specific types with the 

 tropical forms, even though deficient in some of their apparently most 

 important features. The depth of the sea-bottom seems also to affect 

 the prevalence of particular types, and to modify the forms under which 

 they present themselves ; so that Messrs. Jones and Parker feel them- 

 selves able to pronounce approximately as to the depth of water at 

 which a deposit of fossil Foraminifera may have been formed, by a com- 

 parison of its specific and varietal types with those characterizing various 

 depths at the present time. And it is specially worthy of note, that in 

 the greatest depths of the ocean from which Foraminifera have been 

 brought by deep-sea soundings, these belong almost exclusively to one 

 type, Globigerina. 



Now it may be at once conceded that no other group in the Animal 

 kingdom affords any thing like the same evidence, on the one hand, of 

 the derivation of a vast multitude of distinguishable forms from a few 

 primitive types, and on the other, of the continuity of those types 

 through a vast succession of geological epochs. A somewhat parallel 

 case, however, as regards the first of these points, is presented by certain 

 of the humbler groups of the Vegetable kingdom, in which it is becoming 

 more and more apparent, from the careful study of their life-history, not 



* "On some Fossil Foraminifera from Chellaston, near Derby," in the Quarterly 

 Journal of the Geological Society for November, 1860, p. 458. 



