THE FUNCTION OF THE CENTROSOME. 



213 



them, permanent features of these cells, persisting even when 

 the cells are at rest. In the dividing cell the corresponding 

 structures are, as a rule, only transitory. The primary oocyte 

 of Chaetopterus, however, is a remarkable exception to the 

 rule. So long as the oocyte remains in the body-cavity of the 

 worm, it contains a large germinal vesicle and no trace of 

 asters or centrosomes; but, after it has been deposited in sea- 

 water, a typical amphiaster with distinct centrosomes at either 

 pole is developed. If the egg is not fertilized, the amphiaster 



FIG. 5. Diagram of the motor apparatus in the leucocyte and in the muscle-cell (after Watase"). 



on reaching the metaphase (Fig. 4, B) remains in this stage for 

 hours, resembling in persistence, as well as in structure, the 

 motor apparatus of leucocytes and muscle-cells. 



The leucocyte, as is well known, is susceptible to chemotac- 

 tic influences ; certain chemical substances, e.g., those elabo- 

 rated by bacteria, will stimulate the motor mechanism of this cell 

 to normal activity. Likewise, as Mr. Green has proved, isolated 

 portions of the turtle's heart will resume the normal rhythmical 

 contractions upon the introduction of extremely weak solutions 

 of certain salts; e.g., sodium, calcium, potassium and magne- 

 sium. May not the analogous mechanism within the oocyte of 

 Chaetopterus be induced to resume its normal activity upon 

 the introduction of a similar stimulating substance ? 



If this oocyte, in which the maturation spindle has been 

 developed, is placed in a solution of from ^ fo to % fo KC1 in 



