RHIZOPODA. 33 



does not differ from the Amoeba, but the greater part of the 

 body is enclosed in a sort of case or carapace, mostly com- 

 posed of grains of sand, within which the animal can retire 

 completely. The carapace is open at one end, and the pseu- 

 dopodia are protruded from this aperture. The animal gene- 

 rally creeps about head-downward, so to speak ; that is to say, 

 with the closed end of the carapace elevated above the surface 

 on which it is moving. 



ORDER III. FORAMINIFERA (Lat. foramen, an aperture; 

 fero, I carry). The next order of the Rhizopoda is that of the 

 Foraminifera, comprising animals which at first sight appear 

 to be highly complex, but which are really much less highly 

 organized than the Amoeba. The Foraminifera may be de- 

 fined as Rhizopoda in which the body is protected by a shell 

 or " test / " there is no nucleus or contractile vesicle / and the 

 pseudopodia are extremely long and threadlike, and interlace 

 with one another so as to form a net-work. 



The most obvious and striking character of the Forami- 

 nifera is the possession of an outer case or shell, and for a long 

 time they were known to naturalists by then* shells alone. As 

 the shell or test is usually very beautiful and often very com- 

 plex, the Foraminifera were consequently placed at first 

 among the true shell-fish (Mollusca), very much in advance of 

 their true position. When, however, the anatomical structure 

 of the group came to be investigated, it was soon found that 

 they were really referable to the Protozoa, and that in point 

 of fact they even occupy a low position in this sub-kingdom. 

 However elaborate and complicated the shell may be, the body 

 of the contained animal is composed simply of granular gelati- 

 nous sarcode, highly elastic and contractile, and usually red- 

 dish or yellowish in color. This sarcode* not only fills the 

 shell, but also in many cases gains the exterior by means of 

 little perforations in its walls, and forms a thin film over its 

 outer surface. Wherever the sarcode is exposed, whether this 

 be only at the mouth of the shell, as in Miliola (Fig. 4, b), or 

 whether it be over the whole surface, as in Discorbina (Fig. 4, 

 c), it has the power of giving off pseudopodia. The pseudo- 

 podia, however, differ greatly from those of the Amoeba, and 

 they show some remarkable characters. They are extremely 

 long, threadlike processes, instead of being blunt and finger- 

 shaped, and they have the curious property that they run into 

 one another and interlace toward their extremities, so as to 

 form a net-work which has been aptly compared to an " ani- 



