94 W. B. CARPENTER ON THE STRUCTURE OF ORBITOLITES. 



After this I came into possession of some specimens which had 

 been preserved in spirit, and which showed what the animal body 

 occupying these discs really is. Here (Fig. 5) we have its com- 

 posite sarcodic body, belonging to that class to which Dujardin 

 gave the name of Rhizopoda. In the first place there is a primordial 

 segment, a, surrounded by one turn of a large segment, b, forming an 

 imperfect spiral ; this giving off a sort of root-stock, or stolon, from 

 which are budded off rows of sub-segments, that enclose the 

 primordial chambers. Each circle of sub-segments, connected by its 

 annular stolon, corresponds with the segment of an ordinary Fora- 

 minifer ; it is connected by radial stolons with the next annulus ; and 

 the radial stolons of the last-formed annulus issued as pseudopodia 

 from the marginal pores of the shelly disk. The simple disposition 

 of sub-segments in one plane, occupying the single layer of chamber- 

 lets in the minute 0. marginalis, undergoes a very curious modifi- 

 cation in the complex structure of the large 0. complanata, recent 

 and fossil. In this there are two rows of surface-planes, separated 

 by an intermediate plane, the chamberlets of which have a 

 columnar structure (Fig. 6). The successive rows communicate 



Fig. 6. 



Portion of Sarcodic body of Complex Orbitolite : — a a', b b', upper and lower 

 annular cords of two concentric zones ; c c, upper layer of superficial 

 sub-segments ; d d, the lower layer ; e e and e' e\ intermediate columnar 

 sub-segments of the two zones, giving off oblique stolon-processes. 



by a number of oblique threads ; and it is through the 

 threads which issue from the marginal pores of the outermost ring, 

 that the body receives its nourishment. In the living condition 



