FORAMINIFERA AND KAUIOLARIA. 9S 



dead shells which have undergone infiltration with ferruginous silicates. * 

 Here we see that the segments of the sarcode-body are smooth along 

 their anterior edge b, I 1 , but that along their posterior edge, a, they are 

 prolonged backwards into a set of 'retral processes ;' and these processes 

 lie under the ridges of the shell, whilst the shelly wall dips down into the 

 spaces between them, so as to form the furrows seen on the surface. 

 The connections of the segments by stolons, c, c\ passing through the 

 pores at the inner margin of each septum, are also admirably displayed in 

 such * casts.' But what they serve most beautifully to demonstrate is tho 

 canal-system, of which the distribution is here most remarkably complete 

 and symmetrical. At d, d, 1 d,* are seen three turns of a spiral canal 

 which passes along one end of all the segments of the like number of 

 convolutions, whilst a corresponding canal is found on the side which in 

 the figure is undermost; these two spires are connected by a set of 

 meridional canals, e, e 1 , e*, which pass down between the two layers of 

 the septa that divide the segments; whilst from each of these there 

 passes off towards the surface a set of pairs of diverging branches,/,/ 1 , 



FIG. 332. 



Internal Cast of Polystomella craticulata : a, retral processes, proceeding from the posterior 

 margin of one of the segments; 6, &', smooth anterior margin of the same segment; c, ci, stolons 

 connecting successive segments, and uniting themselves with the diverging branches of the 

 meridional canals; d, d\ d\ three turns of one of the spiral canals; e, e 1 , e\ three of the meridi- 

 onal canals; /, /', A their diverging branches. 



/ 2 , which open upon the surface along the two sides of each septal band, 

 the external openings of those on its anterior margin being in the furrows 

 between the retral processes of the next segment. These canals appear 

 to be occupied in the living state by prolongations of the sarcode-body; 

 and the diverging branches of those of each convolution unite themselves, 

 when this is inclosed by another convolution, with the stolon-processes 



1 It was by Prof. Ehrenberg that the existence of such ' casts ' in the Green 

 Sands of various Geological periods (from the Silurian to the Tertiary) was first 

 pointed out, in his Memoir * Ueber den Griinsand und seine Einlauterung des 

 organischen Lebens,' in " Abhandlungen den Konigl. Akad.der Wissenschaften," 

 Berlin, 1855. It was soon afterwards shown by the late Prof. Bailey ("Quart. 

 Journ. Microsc. Sci.," Vol. v., 1857, p. 83) that the like infiltration occasionally 

 takes place in recent Foraminifera, enabling similar 'casts' to be obtained from 

 them by the solution of their shells in dilute acid; the Author, as well as Messrs. 

 Parker and Rupert Jones, soon afterwards obtained most beautiful and complete 

 internal casts from recent Foramimfera brought from various localities; and a 

 large collection of green sands yielding similar casts was made in the * Chal- 

 lenger.' 



