I02 



CELL-DIVISIOy 



precisely like that of muscle-fibres ; and it is difficult to study Bovcri's 

 beautiful figures and clear descriptions without sharing his conviction 

 that "of the contractility of the tibrilke there can be no doubt." ^ 



Very convincing evidence in the same direction is afforded by 

 pigment-cells and leucocytes or wandering cells, in both of which 

 there is a very large permanent aster (attraction-sphere) even in the 

 resting cell. The structure of the aster in the leucocyte, where it 

 was first discovered by Flemming in 1891, has been studied very 

 carefully by Heidenhain in the salamander. The astral rays here 

 extend throughout nearly the whole cell (Fig. 49), and are believed 



_. _ B 



Fig. 49. — Leucocytes or wandering cells of the salamander. [Heidenhain.] 



A. Cell with a single nucleus containing a very coarse network of chromatin and two nucleoli 

 (plasmosomes) ; s. permanent aster, its centre occupied by a double centrosome surrounded by 

 an attraction-sphere. i9. Similar cell, with double nucleus; the smaller dark masses in the latter 

 are oxychromatin-granules (linin), the larger masses are basichromatin (chromatin proper). 



by Heidenhain to represent the contractile elements by means of 

 which the cell changes its form and creeps about. A similar con- 

 clusion was reached by Solger ('91) and Zimmermann ('93, 2) in the 

 case of pigment-cells (chromatophores) in fishes. These cells have, 

 in an extraordinary degree, the power of changing their form and of 

 actively creeping about. Solger and Zimmermann have shown that 

 the pigment-cell contains an enormous aster, whose rays extend in 

 every direction through the pigment-mass, and it is almost impos- 

 sible to doubt that the aster is a contractile apparatus, like a radial 

 muscular system, by means of which the active changes of form are 

 produced (Fig. 50). This interpretation of the aster receives addi- 

 tional support through Schaudinn's ('96, 3) highly interesting dis- 



1 '88, 2, p. 99. 



