336 NATURAL HISTORY. 



The wider, often fingered, and always forward-moving, clear part of the body has been observed 

 to be not so viscid and sticky as the narrower, coarse-grained, food-carrying hinder portion ; and the 

 food has been seen to be taken in by the creeping mass, as it flows on like moving slime, more 

 frequently just about the place where the clear passes into the granular part, than at other 

 parts of the body. Yet even one or more of the pseudopods can take prey by enwrapping it 

 and passing it on to the interior. 



All the granules, whether of partly digested food, or germinative spherules, or protoplasmic 

 atoms, are often seen to stream forward along the middle of the animalcule, encroaching some- 

 times on its clear moiety, and then to return down each side, to be swept forward again, with 

 varying energy, in a kind of circulation or " cyclosis."* But this is associated with the move- 

 ment of the animal, and is not analogous to a systematic blood-circulation. 



The process of digestion or assimilation is as yet a mystery of organic chemistry. The 

 refuse of the food is gradually accumulated in small lots towards the hinder end, and is let out 

 now and then through the clear sarcode of the surface. Germinal granules or zoospores some- 

 times escape at these opportunities. 



When a lobe or pseudopod is pushed out, the miscellaneous particles of the endosarc appear to 

 rush toward the new projection ; but for the most part only the sarcodic granules follow it up and 

 continue the "cyclosis" in its substance. 



The protrusion of a pseudopod is often preceded by an energetic contraction of the pulsating 

 vesicle; and it has been remarked that, though there is no apparent opening in the common 

 Amoeba for the contents of this vesicle to escape outwardly, it is always at or near the 

 surface of the hinder end when emptying itself. In some cases it may force its fluid far among 

 the atoms of the protoplasm, whether as nutritive or excretory matter. It acts best when the 

 animalcule is in good condition ; and then it is that the movements of pseudopods or other 

 superficial parts are seen to follow its contraction. In a large Amoeba with a villose patch at its 

 end, Dr. Wallich thinks it probable that each ruptured vesicle leaves a ragged edge, which hardens 

 too soon for it to be wholly absorbed into the general sarcode, and thus leaves outstanding 

 morsels (villi) of permanently indurated ectosarc. 



There are also visible in the Amoeba one or more of the clear spots already referred to, which 

 do not fill and collapse at regular intervals. These are known as " vacuoles."t Some are "water- 

 spaces," and seem to be relatively persistent ; others are formed temporarily round large particles of 

 food. The following lucid description of such a " food-vacuole," from the pen of Prof. P. Martin 

 Duncan, is especially apt : 



"A large Amoeba with a very delicate endosarc had been feeding on broken-down Confervse, 

 spores, and green cells, when a tolerably large Diatom, a Pinnularia, came in contact with its small 

 end. The scanty diaphane then immediately increased in quantity and flowed over the intruder, 

 which sank, as it were, gradually into the endosarc, and remained in one part of it. After a few 

 minutes had elapsed, a clear space formed in the Amoeba around the prey, which immediately began 

 to move in it backwards and forwards after its usual fashion. The space was evidently filled with 

 water, and therein moved the captured Diatom, apparently in no great discomfort. After long 

 watching, it became apparent that the size of the space, or vacuole, as it is termed, increased, and 

 that the Diatom became stationary and ragged-looking, and, in the course of more than a day, it 

 split and separated into two halves. After this the vacuole disappeared, and the relics of the meal 

 were jumbled up in the group of granules and other digested bits which streamed about in the 

 endosarc. ": 



Dr. Leidy observes that the food of the Amoeba commonly consists of "various Diatoms, 

 Desmids, green unicellar Algse, and spores of the filamentous Algse. Considerable fragments of 

 the latter, such as Oscillaria, Zygnema, &c., are also often seen among the food contents. 

 Occasionally animal forms may be detected in the food materials in the endosarc, among 

 the most common of which are the Rotifers ; and in several instances I have observed 

 with them an unfortunate Arcella, a Difflugia or a Trinema." Dr. Leidy also describes and 



* Greek, cyclos, a circle. t Latin, racuus, empty ; hence a " diminutive," vacuolum. 



1 "Popular Science Review," new series, vol. i. p. 232. 



