THEORY OF FREE CELL-FORMATION. 35 



form. The nucleus is accordingly, in cells of all shapes, 

 that part which is the most constantly found unchanged! 

 There are indeed isolated cases, which lie scattered 

 throughout the whole series of facts in comparative 

 anatomy and pathology, in which the nucleus also has a 

 stellate or angular appearance ; but these are extremely 

 rare exceptions, and dependent upon peculiar changes 

 which the element has undergone. Generally, it may be 

 said that, as long as the life of the cell has not been 



FIG. 3. 



brought to a close, as long as cells behave as elements 

 still endowed with vital power, the nucleus maintains a 

 very nearly constant form. 



The nucleus, in its turn, in completely developed cells, 

 very constantly encloses another structure within itself 

 the so-called nucleolus. With regard to the question 

 of vital form, it cannot be said of the nucleolus that it 

 appears to be an absolute requisite ; and, in a considera- 

 ble number of young cells, it has as yet escaped detec- 

 tion. On the other hand, we regularly meet with it in 

 fully developed, older forms ; and it, therefore, seems to 

 mark a higher degree of development in the cell. Ac- 

 cording to the view which was put forward in the first 

 instance by Schleiden, and accepted by Schwann, the 



Fig. 3. a. Hepatic cell. b. Spindle-shaped cell from connective tissue. <?. Ca- 

 pillary vessel, d. Somewhat large stellate cell from a lymphatic gland, e. Ganglion- 

 cell from the cerebellum. The nuclei in every instance similar. 



