438 FORAMINIFERA, POLYCYSTINA, AND SPONGES. 



again, as we have seen them to be from the surface of the body 

 of the Actinophrys ( 262) ; for they sometimes accumulate in 

 considerable numbers, so as even to choke up a large part of the 

 cavity. The sarcode body is occasionally seen to extend itself, 

 as shown in Fig. 204, around the exterior of the shell; and 

 pseudopodia are put forth from this extension, as well as from 

 the ordinary outlet. Although nothing is certainly known of 

 the mode of propagation of these animals, yet it is probable, from 

 the analogy of the composite forms, that they multiply them- 

 selves by the detachment of gemmae, composed of portions of 

 sarcode, which in time form an envelope or shell. Nothing has 

 been yet seen, that in the least corresponds to a true Generative 

 process. 



285. By far the greater number of Foraminifera are composite 

 fabrics, evolved by a process of continuous gemmation, each 

 gemma remaining in connection with the body by which it was 

 put forth ; and according to the plan on which this gemmation 

 takes place, will be the configuration of the composite body 

 thereby produced. Thus if the bud should be put forth from 

 the aperture of Gromia, in the direction of the axis of its body, 

 and a second shell should be formed around this bud, in conti- 

 nuity with the first, and this process should be successionally re- 

 peated, a straight rod-like shell will be produced, having many 

 chambers communicating with each other by the openings that 

 originally constituted their mouths, the mouth of the last formed 

 chamber being the only aperture through which the sarcode 

 body, thus composed of a number of segments connected by a 

 peduncle or " stolon" of the same material, can now project itself 

 or draw in its food. The successive segments may be all of the 

 same size, or nearly so, in which case the entire rod will approach 

 the cylindrical form, or will resemble a line of beads ; but it often 

 happens that each segment is somewhat larger than the pre- 

 ceding, so that the composite shell has a conical form, the apex 

 of the cone being the original segment, and its base the one last 

 formed. The method of growth now described, is common to a 

 large number of Foraminifera, chiefly belonging to the genera 

 Nodosaria, Dentaliwa, Morginulina, which M. D'Orbigny has 

 ranked together in an order, under the designation of Stichos- 

 tegues ; it is, however, frequently seen also in the advanced stages 

 of growth of such as usually begin upon the spiral plan ; and 

 there are various considerations (into which this is not the place 

 to enter) which satisfy the Author, that the mere direction of in- 

 crease is a character of very subordinate importance in the group, 

 instead of being one of such fundamental value as to serve for 

 the basis of classification. 



286. If each of the successively formed segments, instead of 

 being developed exactly in the axis of its predecessor, should be 

 directed a little to one side, it is obvious that a curved instead of 

 a straight rod will be produced ; and this curvature may increase, 



