CELLS. 41 



Manifold morphological phenomena go hand in hand with 

 these changes, such as the thickenings of the cell-membrane, 

 which have been already adverted to, with laminated depositions 

 upon their inner surface, and even with the formation of pore- 

 canals j as the precipitation in the cell-contents of granules of 

 different sorts, as of pigment, albumen, casein (in the yelk, 

 perhaps in the hepatic cells) ; and as the formation of fat drops, 

 of elementary vesicles, of concretions, crystals, and nuclei. 

 Even movements resembling the cyclosis of plants appear to 

 occur in the cells of the lower animals (seen by me in the cells 

 of the arms of a minute Medusa, a new JEginopsis from the 

 Mediterranean, and of Polyclinum stellatum), and in Protozoa 

 (currents in Loxodes bursaria, contractile vesicles in different 

 genera) ; while, on the other hand, the Brownian molecular 

 movements, i. e. a more or less active tremulous motion of 

 granules without further change of place, which may be 

 observed in many cells under the microscope, most beautifully 

 in the pigment cells of the eye, are also, perhaps, hardly to be 

 reckoned among vital phenomena. 



The nuclei also occasionally, though upon the whole rarely, 

 take part in the changes of the cells. The commonest of 

 these appearances is their becoming clear, as a consequence 

 of the liquefaction of the at first more viscid contents, upon 

 which circumstance it depends that in young cells they are 

 homogeneous, while in the larger they evidently appear to be 

 vesicles. A formation of granules in the nuclei is very rare (see 

 above) ; concretions, colouring matters, and crystals, are also 

 not found here in animals ; on the other hand, the development 

 of the urticating threads in certain animals and that of the 

 spermatozoa, takes place in nuclei. 



In endeavouring to explain the metabolic processes of cells, 

 we must in all cases especially regard the cell-nucleus; for just 

 as it excites the development of the cell, so is it the centre of 

 the currents of the contents, and of the deposits and solu- 

 tions ; but it is not to be regarded as the sole agent, for, firstly, 

 it does not appear why the cell contents should not, like the 

 cytoblastema, become changed of themselves ; and, secondly, 

 the changes of the cell-membrane arc, at all events, more 

 independent, and probably also have a certain influence upon 

 the cell- contents, as the depositions which take place upon it, 



