446 FORAMINIFERA, POLYCYSTINA, AND SPONGES. 



to US in the curious ThalassicoUa,^ discovered by Mr. Huxley, and 

 since observed by Prof Miiller, which seems also to have rela- 

 tions to the Polycystina (§ 292). 



291. The essential simplicity of the animal, aud the absence 

 of anything like structure in the shell, of the Orbitolite, ob- 

 viously place it much lovs^er in the scale than those Foraminifera, 

 which have the segments not only more completely divided, but 

 enclosed in a shell which is itself distinctly organized. Such is 

 the case with Nummulites and their nearest allies among the 

 recent forms. For in these, as will be more fully shown here- 

 after (Chap. XIX), each segment has its own separate envelope 

 of shell, so that the partition between any two adjacent chambers 

 is double ; the chambers are so far cut oiF from one another, as 

 to communicate only by veiy narrow passages ; but means are 

 afforded, by which even the innermost chambers are brought into 

 tolerably direct relation with the exterior. For in this type of 

 structure, we observe that those parts of their walls which look 

 towards the outer surfaces, are perforated with immense numbers 

 of pores resembling those of Fig. 205, but more numerous, 

 minute, and closely set ; and where the walls are thick, these 

 pores are continued as tubes through their entire substance 

 (Figs. 209, 338). However fine they may be, the extraordinary 

 tenuity of the threads into which the sarcode is occasionally seen 

 to divide itself (Fig. 204), shows that this need not be an ob- 

 stacle to the passage of pseudopodial prolongations through them. 

 But further, in the spaces between the walls of contiguous cham- 

 bers, we find a system of large tubes, which make their way 

 directly from the central to the peripheral portion of the disk, 

 and which, communicating on the one hand with the innermost 

 chambers, and on the other with the margin (being extended 

 and carried on to it whenever the previous edge is covered by a 

 new growth), serve to bring the former into a very direct rela- 

 tion with the external sources of supply of nutriment and oxygen. 

 A strikingly developed example of this system of " interseptal" 

 canals is presented in the genus Faujasina (Fig. 209) ;= where the 

 large size of the canals, and the extreme simplicity of their 

 arrangement, enable them to be very readily traced out. In 

 some instances the arrangement becomes extremely complex: 



• See " Annals of Natural History," 2d Ser. vol. viii, p. 433 ; and " Quart. Journ. of 

 MictosG. Science," vol. iv, p. 72. 



2 See Prof Williamson's Memoir on the Faujasina, in the "Transact, of Mieroso. 

 Soc." 2d Ser. vol. i. As the correctness of the account of the interseptal system of 

 canals, which has been given by the Author (in his Memoir on Nummulite, &c., in 

 "Quart. Geol. Journ." Feb. 1850), and confirmed by the researches of Prof W. and 

 himself upon numerous recent types, has been called in question by no less an authority 

 than Prof Schuize, vifho has, in consequence, altogether ignored this important cha- 

 racter in his classification, the Author thinks it right to state, that although the above 

 figure is copied from one of those vi'hich illustrate Prof Williamson's Memoir, yet it is 

 the almost precise counterpart of a section of the same species prepared by himself. 

 The incredulity of Prof. Schuize and others, upon this point, simply depends upon their 

 waftt of aptitude in the preparation of sufficiently thin sections. 



