Mr. H. J. Carter on the Structure of the larger Foraminifera. 247 



they present no appearance of channelling, but, on the contrary, 

 a heterogeneous composition, as regards size, of small pillars and 

 pellets of condensed shell-substance respectively. The marginal 

 cord, on the other hand, is composed of spicules, an inter- 

 spicular substance, and canals, which are more or less arranged 

 in layers respectively, radiating from the centre of the base of 

 the cord (which is straight) to its circumference (which is semi- 

 circular). The spicules overlap each other longitudinally, and 

 the canals form a densely reticulated structure throughout the 

 substance of the cord, whose branches open in all directions 

 upon its surface. As the test arrives at its full growth, the 

 marginal cord is bent down over the last chamber to meet its 

 preceding turn, to which it becomes attached, and the Operculina 

 is thus hermetically sealed. Hence D'Orbigny's original state- 

 ment that the test is without an opening like that of Nautilus 

 and the Ammonites, and without a siphon. 



Canal-sijstem. — The canal-system consists of — 1. Two great 

 spiral canals, one in each horizontal half of the test, which run 

 from its commencement to its termination, and are situated re- 

 spectively on each side of the marginal cord, at its point of junc- 

 tion externally with the spiral lamina, in which line also it opens 

 externally by fine ramusculi, like those of the interseptal canals. 

 2. The interseptal canals, two in each interseptal space, which 

 arise respectively from the great spiral canals of the preceding 

 turn, and terminate on the inner aspect of the cord, close to the 

 chamber, where they divide into branches which join the mar- 

 ginal plexus, the great spiral canals, and open externally on the 

 surface of the cord, respectively. 3. The marginal plexus, which 

 occupies the marginal cord, and is formed of an intricate network 

 of canals derived chiefly from branches of the great spiral and 

 interseptal canals, which network is spread throughout the cord, 

 and, as before stated, opens in all directions over its surface. 

 4. A system of small canals, which open on the surface along 

 the lines of the great spiral canals and interseptal spaces, and 

 are in connexion with the spiral and interseptal canals re- 

 spectively. 



Animal. — This, as was discovered by Dujardin, is a Rhizopod, 

 which fills more or less all the chambers and canals of the test, 

 besides spreading over its surface externally : hence M. D'Or- 

 bigny was not far wrong when he stated, or M. De Ferussac did 

 for him (Ann. des Sc. Nat. t. vii. p. 100, 1826), "que le test de 

 ces petites coquilles etait entierement renferme dans le corps," 

 though he was wrong for the time in taking the rhizopodous 

 extensions for the arms of a Cephalopod, as he subsequently 

 admitted. The chambers consist of cavities of this sarcode, 

 which are more or less filled with propagative spherules, &c, as 



