278 



BIOLOGICAL LECTURES. 



In this connection, it is interesting to notice a structure 

 closely similar to the aster, as described by Grenacher, Greeff, 

 Schulze, and Sasaki in different forms of unicellular organisms 

 (Fig. 6). The peripheral pseudopodia are connected with the 

 cytoplasmic filaments, which converge and meet at the center 

 of the organism, thus forming a huge aster whose fibrils extend 

 through the whole organism. If we suppose, however, that 

 the individual fibrils of the aster in a leucocyte (Fig. 2), or in 



Jig. h, — Brown pigment cell from the pectoral fin of Biennis trigoides (larva), showing the 

 reticular centrosome (C), — the " Centralnetz."— (After Zimmermann.) 



a pigment cell, extend beyond the general outline of the cell- 

 boundary, we shall get the appearance presented by the unicel- 

 lular organism with a large aster whose rays extend through 

 and beyond the mass of the entire organism, as represented in 

 Fig. 6. 



The absence of the centrosome and the aster in a stationary 

 cell, or in cells which show no trace of "nuclear motion" or 

 caryokinesis, and their invariable presence in cells which show 

 some kind of definite movement, make it tolerably certain, 

 then, that they are intimately correlated with the movement 

 of the protoplasm. 



This general observation naturally leads us to consider the 

 mechanism of motion in the muscle cell, in order to see if it 



