THE FORAMINIFERA. 159 



without apparent organisation, capable of changing into a 

 great variety of forms, laying hold of its food without mem- 

 bers, swallowing it without a mouth, digesting it without a 

 stomach, appropriating its nutritious material without absorbent 

 vessels, or a circulating system, moving from place to place 

 without muscles, feeling, if it has the power to do so, without 

 nerves, but in many instances forming shells of a symmetry 

 and complexity not surpassed by those of any testaceous ani- 

 mals. Although the Amceba has no stomach, digestive cavity, 

 or mouth, it is exceedingly voracious. Throwing out its fila- 

 ments or pseudopodia^ it gradually, with their aid, crawls along 

 the bottom of the pond, until it comes in contact with any 

 object suitable for food, such as a diatom or a particle of 

 vegetable matter, when the animal at once commences to 

 envelope the object with its own substance, whereby it be- 

 comes not exactly swallowed, but embedded. When all the 

 digestible matter has been absorbed, the residue is ejected, 

 indifferently from any part, wherever it happens to be nearest 

 to the exterior. 



Several genera of the fresh-water Rhizopoda form a horny 

 case, in which there are openings for the protrusion of their 

 psendopodia. The genus Difflugia forms a transparent horny 

 case, and fixes upon the outside, particles of sand, and the 

 siliceous shells of Diatomacece. Although the animal is of 

 such excedingly low organisation, it exhibits a curious power 

 of choice, never by any chance selecting other than mineral 

 particles ; fixing them, probably when the case is in a certain 

 glutinous condition, with an appearance of order ; in some 

 displaying almost the symmetry of design, smaller grains 

 being selected and neatly fitted into the interstices of larger 



