1888.] MICROSCOPICAL JOURNAL. 5 



ence existing between them.'* Furthermore, to- call the solid particle the 

 nucleus does not add much to our knowledge, because it is far from being 

 such in any true sense. Positively the only thing that approaches an organ 

 is the contractile vesicle, which apparently plays a part in excretion. This 

 is the strange feature of the Rhizopods ; they have no organs or members of 

 any kind ; no mouth, no stomach, no feet, no tentacles, no anything. They 

 are merely structureless protoplasm ; and when they want feet or tentacles 

 they let some portion of the body flow out in root-like processes, from which 

 characteristic, indeed, they derive their name, the Rhizopoda or root-footed. 

 And yet these structureless creatures can do all that any higher animal can 

 do with all its organs ; for they move, they capture and devour prey, they 

 take in and assimilate food, they grow, they build up shells of exquisite 

 beauty, and they I'eproduce their kind. Thus they are perfect anomalies, 

 enough to puzzle all who study them. Here you have protoplasm at once 

 at its simplest and its best, and a very wonderful substance it is seen to be, 

 with chemical properties most diverse, producing a denser kind of itself, as 

 it were, as in the nucleus, and depositing ' membranes of pure chitin . 

 or shells of pure calcium carbonate or quasi-crystalline needles of silica. 't 

 How it can perform all these various functions — move, seize, eat, digest, grow, 

 and reproduce its kind — without organs of any kind, without even muscle or 

 nerve, is the mystery of mysteries of biology. And here let me remark that 

 the essential part of all the Rhizopods is this protoplasmic substance. I em- 

 phasize this point because it is likely to be overlooked by the novice. What 

 strikes one particularly in very many of the species is the shell or membrane, 

 and the beginner is almost sure to regard that as the prominent featui-e. On 

 the contrary, the shell goes for nothing, so far as the whole class is concerned, 

 it being free and entirely separable from the cell-protoplasm. J It is the sub- 

 stance zvithin the shell that is of paramount importance, and this substance 

 is absolutely the same throughout all the members of the group. The proto 

 plasm and the contractile vesicle, therefore, are the only two features of which 

 we really need to take notice in the study of these forms, for the exact nature 

 of the nucleus is still under discussion, it being doubtful whether it is identical 

 with the nucleus of tissue-forming cells. 



Concerning the first, then, protoplasm, the most prominent characteristic 

 is its motion. This is of a streaming or flowing nature, and is best seen in 

 Amoeba. The whole mass is in a state of ceaseless movement. And this 

 leads to external change of shape as well as internal circulation. In the veg- 

 etable cell the bounding cell-wall prevents any variation of form, and the 

 protoplasm travels round and round the inner side of the investing membrane ; 

 but in the naked rhizopod there is no cell-wall, properly speaking, and the 

 protoplasm pushes out in every direction, followed by a streaming of the more 

 granular and fluid contents. Thus A?)iceba proteus is never the same in shape 

 for any length of time. Try to draw it, and before you have finished it is al- 

 tered in outline. It goes creeping along, this way and that, and suddenly 

 there is a bulging out of the hyaline boundary which quickly lengthens into 

 a finger-like process, or pseudopod, into which the granular portion streams 

 with greater or less activity as the case may be. But even while this is going 

 on, another pseudopod may have formed in the opposite direction, and now 

 the protoplasm flows back into that. If an ' animalcule ' or a desmid comes 

 in contact with one of these pseudopods others are quickly put out on that 

 side of the body, as a fisher might cast his lines, and these gradually close 

 round the prey in such wise as to form a temporary stomach. Digestion at 

 once begins, and after all the nutriment has been assimilated the protoplasm 



* Ency. Brit., Protozoa. ^ Ency. Brit., Protozoa. XEncy. Brit., Protozoa. 



