THE CELL. 19 



lobed, or even seemed to disappear altogether before cell-division. A 

 few years later, it was seen that the process of division was compli- 

 cated in the extreme, and that the cell-nucleus underwent a variety of 

 transformations, assuming different shapes and figures until two 

 daughter-cells were formed from the mother-cell. This process was 

 afterward named karyokinesis. 



By experiment, it was demonstrated that, if a cell in a living 

 organism or tissue was so divided that one of the parts was composed 

 of protoplasm only, none of the nucleus being present, the proto- 

 plasmic part continued to live for a considerable time, but that, of 

 the vital phenomena exhibited by the normal cell, it possessed only 

 that of movement. It was unable to take up from the surrounding 

 tissues a proper amount of nutrition, so that growth and reproduc- 

 tion never occurred, and after a time it died. Thus it was concerned 

 only in destructive, not constructive, metamorphosis. It was totally 

 unable to build itself up, to grow, or reproduce others of its species. 

 On the other hand, the part containing the nucleus grew and repro- 

 duced its kind, forming daughter-cells, that in turn formed other 

 cells, etc. 



Thus, in order that the daughter-cell may possess the same 

 properties, form, and functions of the mother-cell, in a word, in 

 order that it may live, it becomes necessary, in the division, that 

 both the nucleus and the protoplasm must divide. The disposition 

 of any cell to divide, or reproduce, is usually announced by changes 

 in its nucleus, both physical and chemical. In fact, the division of 

 any cell is preceded by division of the nucleus. This process in the 

 cells of most organisms is very -complicated, whereas the division of 

 the protoplasm is most simple, consisting of the appearance of a con- 

 striction, which becomes deeper and deeper, forming a groove, or 

 fissure, until eventually the mass is divided into two parts. 



The evident importance of the relation of the nucleus to cell- 

 division has led to extended study of the nucleus and its transforma- 

 tions during the process of reproduction, with the result that, upon 

 its function in this respect, threv forms of division are recognized: 

 (1) direct cell-division, (2) indirect cell-division, and (3) endogenous 

 nuclear multiplication. 



i. Direct Cell-division (Amitosis). 



Direct cell-division is very rare, and present only in some of the 

 unicellular organisms and leucocytes. In pathological formations, 

 however, such as tumors, this form of division occurs very frequently. 



