I02 



CELL-DIVISION 



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

 beautiful figures and clear descriptions without sharing his conviction 

 that "of the contractility of the fibrillas 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 disco^'ered 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 



A .^-^ 



Fig_ 4Q. _ 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. B. Similar cell, with double nucleus ; the smaller dark masses in the latter 

 are o.xychromatin-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. 



