276 



BIOLOGICAL LECTURES. 



(i) Inquiries into different forms of the centrosome and 

 its structural correlations with functions of cells in which it 

 occurs. 



(2) To see if, among the hitherto recognized elements in 

 the cell, there is any structure which shows affinity to or iden- 

 tity with the centrosome. 



Whatever conclusion may be reached as to the value of two 

 rival forms of theories, it seems pretty certain that the exist- 

 ence of the centrosome and its aster is closely correlated with 

 the phenomena of definite movements of the protoplasm. 



Thus, in the caryokinetic process of the cell, which is pre- 

 eminently a phenomenon of protoplasmic motion, the centro- 

 some or its equivalent is invariably present (Fig. i). In the 

 leucocyte, which has a highly developed power of protoplasmic 

 motion, the aster and its centrosome are well developed (Fig. 2). 

 In the pigment cell, in which motor phenomena are well known, 



. the centrosome and its aster 

 find their most remarkable de- 

 velopment (Fig. 3). In some 

 pigment cells with circular out- 

 lines, the aster with its centro- 

 some assumes an ordinary stel- 

 late form. In elongated pig- 

 ment cells, the centrosome, in- 

 stead of assuming a spherical 

 shape, is elongated or rod-like, 

 with a fringe of cytoplasmic 

 filaments proceeding from it 

 (Fig. 4, b). In still another, 

 form of the pigment cell, the 

 centrosome assumes neither the 

 spherical nor the rod-like shape, 

 but exhibits an extensive network conforming to the general 

 shape of the cell (Fig. 5, C). 



On the other hand, in fixed cells with no power of definite move- 

 ment, such as gland cells or cartilage cells, we have no evidence 

 of the existence, either of the centrosome or of the aster, in 

 any part of the cell. If such cells are artificially injured in 



C- 



Fig. 2. — The leucocyte of Salamander, 

 showing the radial system of cytoplasmic fila- 

 ments (aster), and the distribution of the mi- 

 crosome {RT). C, centrosome ; N, nucleus. 

 — (After Martin Heidenhain.) 



