386 PROF. TH. W. ENGELMANN. 



often quite different in immediately neighbouring spots. The 

 threads can divide, fuse, and form sheets, and generally exhibit 

 streaming granules, and behave on the vrhole like the pseudo- 

 podia of Rhizopods (see above). This type occurs in numerous 

 vegetable cells, in hairs from plants (Cucurbita, staminal 

 hairs from Tradesc antia, fig. 2, &c.). It also occurs in 

 Noctiluca, Dicyema (Entoderm cells), in the cartilaginoid 

 cells of the tentacles in Medusae and in the gill-fibres of 

 Branchiomma, in enchondroma-cells, &c. 



Rotation. — The protoplasm lining the walls of a cell (the 

 outermost pellicle excepted) rotates as a connected mass 

 around the interior of the cell, generally following constant 

 tracks and with an even velocity. The direction of the move- 

 ment is always one almost parallel to the long axis of the cell. 

 Any protoplasmic contents which may exist — nuclei, chloro- 

 phyll granules, crystals — rotate along with it, generally with- 

 out changing to any considerable extent their relative position. 



The best known instances of this movement are the cells of 

 the Characese, the leaf-cells of Vallisneria spiralis and 

 Ceratophyllum submersum, and the root hairs of Hy- 

 drocharis morsus-ranse. 



Here must also be classed the rotation of the endoplasm of 

 ParamcEcium bursaria and P. aurelia and some other 

 Infusoria (e.g. Vorticellse). 



IV. General Conditions of Spontaneous Protoplasmic 

 Movement.' 



1. Temperature, 



For every contractile protoplasm there is a lower and a higher 

 temperature at which its spontaneous movements stop, directly 

 and under all circumstances. The minimum generally lies at 

 about 0° and the maximum about 40° C. Within these two 

 temperatures is the province of manifest contractility ; and the 



> Most important literature : — Dutrochet, ' Compt. rend.,' ii, pp. 775 — 784, 

 1837 (Chara) ; Max Schultze, ' Das Protoplasma der Rhizopoden, &c.,* 

 1803 ; W. Kiilme, ' Unters. iiber das Protoplasma, &c.,' 1864. 



