FORAMIXIFERA. 107 



ject made by Mr Henry Bowman Brady, F.R.S., one of the 

 highest living authorities on this group of organisms ; since 

 they not only have a most important bearing upon the 

 special point in question, but forcibly express the principles 

 which should guide the philosophic naturalist in his syste- 

 matic treatment of all such variable forms of life : "A 

 purely artificial classification is ill adapted to the conditions 

 presented by a class of organisms like the Foraminifera, 

 largely made up of groups of which the modifications run in 

 parallel lines. This 'isomorphism,' demonstrated chiefly by 

 the labours of Messrs Parker and Jones, whilst it is the 

 source of most of the difficulties the systematist has to con- 

 tend with, is, at the same time, the key to the natural his- 

 tory of the order. It exists not merely between a single 

 series, say in one of the larger divisions, with a single series 

 in another, but often amongst several series even of the same 

 family. It not unfrequently happens that a member of one 

 group presents a greater similarity to its isomorph in another 

 group with which it has a relationship, than it does to any 

 other member of its own group. Take a familiar illustration 

 suppose the fingers of the two hands to represent the 

 modifications (' species ') of two such parallel types of Fora- 

 minifera : the thumb of one hand resembles more closely the 

 thumb of the other hand than it does any other of the fingers 

 on its own. In other words, the extreme member of one 

 series resembles more closely its isomorph in the other series 

 than it does its own nearer relations, and so on through the 

 remaining members of the respective groups. Under condi- 

 tions like these, artificial subdivision, based upon minor mor- 

 phological characters; is certain to infringe the order of 

 nature. Its tendency is to separate forms closely allied, 

 and in many cases to place together such as have no close 

 affinity." 



The principal fossil groups of Foraminifera deserve a brief 

 consideration, but in the short summary of these which 

 follows as in the case of similar summaries which will 

 subsequently be given it must be understood that nothing 

 further is proposed than to select for notice and characterisa- 

 tion those leading types of each great group of fossils which 



