254 REPORT OF NATIONAL MUSEUM, 1897. 



nutritive portion. To furth'er account for the necessary food supply, it 

 is believed that the Foraminifera absorb organic matter held in solu- 

 tion by the sea water. This theory is the more easily accepted since 

 we know that they have the power to separate inorganic matter (car- 

 bonate of lime in particular) from its solution, with which to construct, 

 wholly or in part, their shells. 



Of the process of reproduction little is known beyond the fact of 

 multiplication by gemination and fission. Every part of this simple 

 animal being sufficient unto itself for purposes of nutrition and growth, 

 it follows that a fragment of the protoplasmic body cast off from the 

 parent becomes at once a new individual and the possible founder of a 

 fresh colony. But it is not in accord with what we know of the life 

 histories of other living things that this process of subdivision or prop- 

 agation by cuttings or shoots can go on indefinitely. It is more likely 

 that some kind of sexual reproduction takes place, the manner of which 

 is yet to be demonstrated. 



The most striking characteristic of this simple, semifluid animal, of 

 indefinite and changeable shape, is its ability to construct a shell or 

 test of definite form in which to shelter itself. This shell or test may 

 be irregular, simple, and rude in construction, or symmetrical and of 

 great delicacy and beauty, in variety of forms rivaling the shells of the 

 Mollusca, of which it was long thought to be a diminutive example. 



Structurally there are three quite definite and distinct types of tes- 

 taceous covering. The first, to begin with the lowest and least common, 

 is the "chitinous" test a thin, transparent, yellowish or brownish 

 membranous investment secreted by the animal. It has one or more 

 general apertures, but is not perforated with fine foramina, and there 

 is no means of communication between the inside and outside of the 

 test except by the general apertures. The foraminifera with this kind 

 of shell have been grouped in the single family of Gromidce. As a rule 

 they inhabit only fresh or brackish water. They have not been found 

 in deep-water marine collections, and do not appear in the following 

 catalogue. 



The second type is the so-called "arenaceous" test. This is an 

 investment constructed of grains of sand, or of the dead shells of other 

 foraminifera, or of sponge spicules, or even of mud, cemented together 

 more or less firmly by means of a calcareous cement secreted by the 

 animal. Usually it has one or more general apertures of comparatively 

 large size, and in addition there may be minute orifices between the 

 sand grains, or other substances of which the test is constructed, 

 through which the delicate threads of protoplasm can be projected. 

 The surfaces may be rough and coarse or smooth and highly finished, 

 according to the fineness of the material used and the amount of cement 

 deposited in the crevices and angles between the grains. When con- 

 structed of mad these tests are found, in some instances, to have a 

 chitiuous base, which maintains the shape of the investment. 



