578 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINTFEEA. 



destitute of them (as Professor WILLIAMSON has pointed out in Potystomella crispa); 

 and such forms differ much less widely, as regards this character, from the simpler 

 forms of Calcarina, than these last do from the very complex forms which have been 

 shown (^[ 197) to be connected with them by a continuously gradational series. Hence 

 I cannot regard the remarkable development of the supplemental skeleton in Calcarina 

 as affording any disproof of the idea of its genetic relationship to Rotalia, to which its 

 affinity in every other particular is most intimate. 



250. If, again, we inquire into the import of that remarkable development of the 

 canal-system, which seems to be the distinctive feature of Polystomella, we find that if 

 we base our judgment upon a sufficiently wide foundation of facts, its non-essential 

 character becomes apparent. For although the large P. craticulata of the tropical and 

 Australian seas presents the most symmetrical and extensive distribution of the canal- 

 system that I have anywhere met with (^[ 187-191), the little P. crispa of our own 

 seas exhibits but feeble traces of it (^f 192) ; yet of the intimacy of their relationship 

 no doubt can be fairly entertained. We have traced a parallel difference between the 

 gigantic Amphistegina Cumingii and the comparatively diminutive A. gibbosa (*jf 171). 

 And the like difference has been shown to exist between the two forms of Tinoporus 

 (^[ 222), where its presence or absence is obviously associated with the presence or 

 absence of the radiating prolongations and of the supplemental skeleton from which 

 these proceed. 



251. In considering the import of the canal-system as a character for the systematist, 

 the mode of its formation must not be left out of view. I have shown that the passages 

 which altogether go to make up this system are not true vessels, but are mere sinuses, 

 left in some cases by the incomplete adhesion of the two contiguous walls which sepa- 

 rate the adjacent chambers, and in other cases apparently originating in the incomplete 

 calcification of the sarcode which forms the basis of the solid skeleton ; certain portions 

 of that substance remaining in its original condition, so as to maintain a communication 

 between the contents of the chambers and the parts of the calcareous skeleton most 

 removed from them, analogous to that which the Haversian canals afford in the case of 

 laminae of bone not in the immediate vicinity of a vascular surface. As, therefore, the 

 development of the Haversian system is related to the thickness of the bone-substance 

 to be nourished, so does that of the canal-system in Foraminifera seem to be related to 

 that of the consolidating substance which constitutes the supplemental skeleton. And 

 it is to be specially observed that nearly all the forms in which (so far as we know at 

 present) it attains any considerable development, are denizens either of tropical or of sub- 

 tropical regions, in which the influence of external conditions appears specially to favour 

 the largest growth and the most specialized evolution of the Foraminiferous type. 



252. I think it better, in the present limited state of our knowledge of two of the 

 types to the elucidation of whose structure the present memoir has been devoted, viz. 

 Tinoporus and Carpenteria, to forbear to speculate further than I have already done 

 upon their relationship to the forms already familiar to systematists (^[ 217, 230). 



