THE CELL. :>.-, 



Attraction sphere, protoplasmic radiation, or archoplaxtn. Tin- 

 significance and relations of the centrosome during the nuclear 

 and cell division will be spoken of later. 



We have considered above all the constituent parts of the 

 cell at rest. It is necessary now to discuss briefly the living 

 properties of the cell in so far as they can be studied by the 

 direct help of the microscope. 



The reader may extend his information on this subject in 

 more exhaustive works in which the cell is treated also from a 

 physiological standpoint (O. Hertwig, Verworn, Bergh). 



The different powers and properties of the cell we can group 

 under : 



1. Those of motion ; 



2. Those of irritability ; 



3. Those of assimilation and excretion ; 



4. Those of reproduction. 



1. The first function which the cell can fulfil i. <?., motility 

 seems to be dependent only 011 the protoplasm ; for portions of 

 this separated from the nucleus are capable of motion for some 

 time. We may speak of various kinds of motion : 



Lymph corpuscle of the frog, studied on a warm stuuc. The outline of the cell has IHM-M 

 inside at intervals of two minutes. One vsicuole is to he seen. 1">00. 



(a) Amoeboid movement consists in the protrusion of proc- 

 esses (pseudopodia) by the protoplasm, which draw the rest 

 of the cell after them. The pseudopodia may also be drawn 

 back to the cell again. If we observe under the microscope 

 such cells or unicellular organisms which have the property of 



