1 6 THE ANIMAL CELL. [CH. II. 



The amoeboid movements of the colourless corpuscles of the 

 blood may be readily seen when a drop of blood from the finger 

 is mixed with salt solution, and examined on a warm stage with 

 the microscope. If a pseudopodium of such a corpuscle is 

 observed under a high power, it will be seen to consist of hyalo- 

 plasm, which has flowed out of its spongy home, the reticulum. 

 Later, however, a portion of the reticular 

 part of the protoplasm may enter the 

 pseudopodium. The cells may be fixed 

 by a jet of steam allowed to play for a 

 moment on the surface of the cover glass. 

 The next figure illustrates one fixed in 

 this way. 

 Fig. 17. An Amoeboid cor- The essential act in the protrusion of a 



puscle of the newt killed , j . , , n < , i i i 



by instantaneous appii- pseudopodium is the flowing of the hyalo- 

 th^appe^e 8 ^! P.^m out of the spongioplasm ; the retrac- 

 pseudopodia. (After D. tion of the pseudopodium is a return of 



Gunn, Quain's Ana- ,,111 i mi 



tomy.) the hyaloplasm to the spongioplasm. Ihe 



spongioplasm has an irregular arrangement 



with openings in all directions, so that the contractility of undif- 

 ferentiated cells may exhibit itself towards any point of the compass. 



Cell Division. 



A cell multiplies by dividing into two ; each remains awhile in 

 the resting or, more correctly, non-dividing condition, but later it 

 grows and subdivides, and the process may be repeated indefinitely. 



The supreme importance of the cell, the growth of the body from 

 cells, and the fact that cells are the living units of the organism, 

 were first established in the vegetable world by Schleiden, and 

 extended to the animal kingdom by Theodor Schwann. The ideas 

 of physiologists depending on this idea are grouped together as 

 cellular physiology, which under the guidance of Virchow was 

 extended to pathology also : Virchow expressed the doctrine now 

 so familiar as to be almost a truism in the terse phrase omnis 

 cellula e cellula (every cell from a cell). 



The division of a cell is preceded by division of its nucleus. 

 Nuclear division may be either (i) simple or direct, which consists 

 in the simple exact division of the nucleus into two equal parts 

 by constriction in the centre, which may have been preceded by 

 division of the nucleoli ; or (2) indirect, which consists in a series 

 of changes which goes on in the arrangement of the nuclear 

 reticulum, resulting in the exact division of the chromatic fibres 

 into two parts, which form the chromoplasm of the daughter nuclei. 



