CAB OM THE AliiJANi.KMii.vr OF THE BHIZOFODA. Ki'.t 



instead of after, their detachment from it, can pcftrcejyW admitted by 



the Physiologisl as alone justify ing a:i ordinal ditl'crciit iat ion, which 



is not borne out by other structural or physiological diversities. 



Having shown in my former paper how completely fallacious is 

 the assumption of M. IVOrbigiiy that plan of growth affords the 

 key to the natural arrangement of Foraniinifera,---rai3ty classification 

 that is founded upon it necessarily bringing together generic types 

 which are physiologicalfy most distinct, and separating such as are 

 physiologically most nearly allied, — I shall now confine myself to a 

 concise exposition of what appear to me the principles on which 

 Natural Classification should be founded. 



Looking at the Order Keticulauia as a whole, the only great 

 physiological distinction at present known to exist among the multi- 

 tudinous forms of animal life which it includes (our acquaintance 

 with the mode in which the generative function is performed in this 

 group being as yet so imperfect, that no differential characters can 

 be founded upon it), is that presented by the two modes in which 

 the pscudopodia originate, viz. : — either from the surface of the body 

 generally, or from a limited portion of it. The animals of the former 

 type, of which Botulia may be taken as an example, have a shell 

 whose surface is everywhere perforated with numerous closely set 

 pores ; and through these, as observation shows, the pscudopodia 

 extend themselves freely from each of the segments that occupies the 

 subjacent chambers. In those of the latter, of which Miliola may be 

 taken as the type, the walls of the chambers are entirely imperfora- 

 ted ; so that the pseudopodia can only issue from the single or mul- 

 tiple aperture, which leads to the last-formed chamber alone. The 

 fundamental importance of this distinction was perceived (as I have 

 already pointed out) by Dujardin ; and my own. enquiries, which 

 have been pursued on a basis altogether independent of his, have led 

 me most fully to recognize the merit of that far-sighted perception, 

 which would have been more likely to attract the notice it deserved, 

 if its author had been aware that, instead of being isolated from the 

 true Foraminifera by the characters in question, the Miliola are 

 really the representatives of that large group of Foraminifera which 

 are distinguished by the porcellanous texture of their shells. 



Taking our stand, then, upon the limitation or diffusion of tho 

 origin of the pseudopodia— manifested in the imperforat ion or the 

 perforation of the testaceous envelope,^ — as a distinction of funda- 

 mental importance, we find that the Order Eetki i,ai;l\ may be sub- 

 divided by this character into two sections; and as it is) ronwnient 

 to base our systematic arrangement of the l'oraminifora upon the 

 characters furnished by the shell (though always hearing in mind that 

 these are of value only in so far as they may be taken as exponents of 

 the characters of the animal) these two sections or sub-orders maybe 

 respectively designated Impekeokata and Plkiokata. 



In the sub-order Impebfohata, the testaceous envelope pr 

 itself under three very different conditions, the membranous, thepor- 

 cdlanous, and the arenaceous ; and upon this difference we may 



