X PREFACE. 



of the sea-bottom seems also to affect the prevalence of particular types, and to modify the 

 forms under which these present themselves ; so that Messrs. Parker and Rupert Jones feel 

 themselves able to pronounce approximately as to the depth of water at which a deposit of 

 fossil Foraminifera may have been formed, by a comparison of its specific and varietal types 

 with those characterising 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, Glohigerina, one of the most 

 simple of the Polythalamia. 



In applying the results of the foregoing inquiry to the Animal Kingdom generally, it 

 may be at once conceded that no other group affords anything like the same evidence, on the 

 one hand of the derivation of a 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. But a nearly parallel case, as regards the first of these points, is pre- 

 sented 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 only that their range 

 of variation is extremely wide, but that a large number of reputed genera and species have 

 been erected on no better foundation than that afforded by the transitory phases of types 

 hitherto known only in their states of more advanced development. It would be very un- 

 reasonable to put aside these cases as so far exceptional, that no inferences founded upon 

 them can have any application to the higher forms of Animal and Vegetable life. For it is 

 only in the extent of their range of variation, that Foraminifera and Protojihyta differ from 

 Vertehrata and PUanerogamia ; and the main principle which must be taken as the basis of 

 the systematic arrangement of the former groups — that of ascertaining the range of variation 

 by an extensive comparison of indi\adual forms — is one which finds its application in every 

 department of Natural History, and is now recognised and acted on by all the most eminent 

 Botanists, Zoologists, and Palaeontologists. 



The following are the general propositions which it appears to me justifiable to base on 

 the researches of which I have now given a resume : 



a' 



I. The range of variation is so great among Foraminifera, as to include not merely the 

 differential characters which systematists proceeding upon the ordinary methods have 

 accounted specific, but also those upon which the greater part of the genera of this group have 

 been founded, and even in some instances those of its orders. 



II. The ordinary notion of species, as assemblages of individuals marked out from each 

 other by definite characters that have been genetically transmitted from original proto- 

 types similarly distinguished, is quite inapplicable to this group ; since even if the limits of 

 such assemblages were extended so as to include what would elsewhere be accounted genera, 



