PROTOPLASM AND NUCLEUS. ng 



a more minute investigation, they are only mentioned here ; the next section will 

 be specially devoted to them. 



The external configuration of the protoplasm into a definitely formed body 

 can be reduced to two cases : — either its single smallest particles are constantly 

 grouping themselves concentrically around a common centre, or an internal 

 motion takes place, which causes the protoplasmic body to become elongated in 

 some one direction, and disturbs the centripetal arrangement. The former oc- 

 curs commonly in the formation of new cells, the latter in their grow^th. 



The movements of the smallest particles of protoplasm which bring about 

 its grouping and configuration in the formation and growth of cells, are generally 

 so slow as not to be visible even when the cells are very highly magnified. Much 

 quicker movements, even appearing rapid under a very high magnifying power, 

 occur in cells already formed, more or less independently of their growth, and either 

 preceding it (as in swarm-spores) or following it. As to the external appearance, 

 the following kinds of movements of this nature may be distinguished : — (A) Move- 

 ments of naked, membraneless protoplasmic bodies, (i) The sivimming of swarm- 

 spores and spermatozoids ; this is characterised by the naked protoplasmic body, 

 swarm - spore or spermatozoid, not changing its external form, while motile 

 vibratile cilia, themselves probably thin threads of protoplasm, cause rotation 

 round the longer axis, and at the same time a progressive movement in the water. 

 (2) Amccba-movement ; — consisting of rapid changes of the external contour of 

 naked protoplasmic structures, Myxoamoebae and Plasmodia, which, supported under 

 water or in the air on a firm moist body, creep about as if flowing, extending 

 and contracting ; while within both the principal mass and the appendages which 

 proceed from it, 'streaming' motion occurs. (B) Movements of the protoplasm 

 within the cell- wall ; this occurs after the protoplasmic body of the cell has 

 formed a larger sap-cavity, and continues commonly after the grow^th of the cell 

 has ceased until the end of its life. (3) Those movements are distinguished 

 as Circulation when strings and bands, proceeding from the parietal protoplasm, 

 run to that portion which envelopes the nucleus, and often stretch completely across 

 the sap-cavity. A distinction is drawn between mass-movements of larger portions 

 of protoplasm, and streaming movement of the substance of which they are com- 

 posed ; the former consist in accumulation or diminution of the parietal layer, 

 wanderings of the mass which contains the nucleus in difi"erent directions, and, 

 dependent on this, of different groupings of the strings. Within these structures 

 of the body of the cell itself streamings often occur, which are apparent from the 

 movement of the enclosed granules, often in opposite direcdons within the same 

 thin string. In the cells of lower and higher plants which are rich in protoplasm 

 and sap but poor in granular contents, the circuladon is a widely distributed phe- 

 nomenon, especially visible in the hairs. (4) The term Rotation is applied to those 

 movements where the whole mass of protoplasm enclosing a cell-cavity circulates 

 on the cell-wall as a thick current complete in itself, and carries along with it 

 the grains and granules contained in it. This occurs in some water-plants, 

 Characeae, Vallisneria, root-hairs of Hydrocharis, &c. 



(a) The protoplasm shows two conditions, which may be distinguished as the living 

 and the dead; the former passes over into the latter by the most various chemical 



