578 
DE. CAEPENTEE’S EESEAECHES OX THE FOEA^nXlEEEA. 
destitute of them (as Professor Williamson has pointed out in Polystomella crispa)\ 
and such forms ditfer 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 CaJcarina 
as affording any disproof of the idea of its genetic relationship to Eotalia, to which its 
affinity in every other particular is most intimate. 
260. 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 ti'opical 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 (^192) ; yet of the intimacy of their relationship 
no doubt can be fairly entertained. We have traced a parallel difierence between the 
gigantic AmpMstegina Cumingii and the comparatively diminutive A. gihhosa 
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 Hew. 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 commimication 
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 memoh has been devoted, ^iz. 
Tinoporus and Garpenteria, — to forbear to speculate further than I have already done 
upon their relationship to the forms already familiar to systematists (^^ 217, 230). 
