ORIGIN OF THE CLEAVAGE CENTROSOMES. 



223 



positive evidence that they are directly derived from egg and 

 sperm centrosomes. 



If now the eggs of Crepidula planet which have given off the 

 second polar body but a short time before are brought for four 

 hours into a I per cent, solution of NaCl in normal sea water 



FIG. i. 



FIG. 2. 



FIG. 



FIG. 4. 



FIGS. 1-4. Eggs of Crepidula flana treated with I per cent. NaCl in sea water 

 for four hours, viewed from the side. In all the eggs the polar bodies are at the 

 upper pole, the egg nucleus and centrosome, or spindle, immediately below this, 

 while the sperm nucleus lies in a small area of cyptoplasm near the lower pole. 

 Various stages in the formation of the egg spindle are shown. 



they will present the appearances shown in Figs. 1 12. These 

 figures are camera drawings of eggs in different stages of the 

 formation of the first cleavage spindle and all are from the same 

 experiment. 



An examination of these figures shows that various stages in 

 the division of the egg centrosome occur (Figs. 1-5) leading to 



