BY W. J. BYRAM. IX 



is SO plastic that it undergoes many Protean changes as it 



slowly creeps across the glass, beneath which it is placed for 



examination. It is a remarkable fact, however, that the amagba 



sometimes passes into what is known as the encysted state : 



that is, it draws in all its processes, assumes an oval shape, and 



secretes a cell wall. In this condition it greatly resembles a 



plant cell. From such observations as these it became evident 



that an error had been made in the generalisation that the cell 



is an enclosed vesicle, for here we meet with the unit existing 



in its ordinary state without any limiting membrane, and the 



study of animal histology has disclosed the fact that, just as 



vegetable cells usually possess well marked cell walls, the reverse 



is the rule with animal cells, which commonly lack the cell wall 



altogether. When the theory was revised in the light of these 



revelations it was, of course, at once apparent, that not only 



was the term "cell" a misnomer, as applied to the biological 



unit generally ; but, as a large number of cells are entirely 



■destitute of the cell wall, that part of the cell could not 



only no longer be looked upon as the most important, but 



where it exists, must be regarded as quite subsidiary. 



These discoveries and consequent change of aspect in the theory 



gave rise to developments which have been of the utmost 



significance in the progress of biology. Biologists fixed their 



attention on the cell contents, and the result was that the cell 



theory entered upon a new phase, which so changed its whole 



aspect, that it might almost be enunciated afresh and termed 



the protoplasmic theory. In his researches Schleiden, while 



assigning the primary importance to the cell wall, had not 



overlooked the fact that many of the cells which he examined 



contained a semi-flaid substance interspersed with granules. 



To this he gave the name of plant slime. Later on this 



substance was designated protoplasm, or primary formative 



substance ; and it was found to possess characteristic movements, 



and to be most abundant in very young cells and more scanty in 



older ones. A similar glairy, contractile substance had been 



observed in animal cells, and called sarcode or elementary flesh. 



This substance was readily studied in the microscopic marine 



animals known as radiolara and foraminifera ; for these forms 



consist of single units enclosed in minute tests or shells of 



carbonate of lime, and when in a state of activity they put out 



their substance in the form of lengthened processes from the 



numerous little pores which exist in their shells. Indeed they 



seem almost to imitate the magic of Ariel, and to be able to 

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