Centrosome ijj Ejiucleated Egg-Fragments. 



303 



water for twenty-two minutes after the first maturation mitosis 

 reached the metaphase. The centriole is here obscured by the 

 strong rays. Striking is the similarity between Figs. 16 and 17. 

 {cf. Morgan, '99, PI. 10. Figs. 54c, 55, 57-MgCl2, and Fig. 

 63-NaCl.) The strong-rayed asters seem to be due to the 

 pecuhar action of MgCL on the egg of Cerebratulus. Further 

 experiments are necessary to find out w^hether the centrioles 

 are produced by M^gClg. 



14 a 



14b 



Fig. VIII (X903). 



14a, Cytaster from section of the fragment shown in Fig. 13a. J^t, central aster of the first 

 maturation figure, modified by MgCl2 solution. 



IV. EXPERIMENTS ON THE EGG BEFORE THE DISSOLUTION OF 

 THE GERMINAL VESICLE. CaClj SOLUTION, HEAT-STER- 

 ILIZATION. 



To determine whether the cytasters are produced by the CaClz 

 solution before the dissolution of the germinal vesicle the follow- 

 ing experiments were carried out: 



In 1903 ten enucleated fragments were cut from the eggs just 

 released into water and were treated with the CaClz solution. 

 No cytasters appeared in any of these fragments. 



In 1904 three parallel experiments were made on the egg 

 fragments taken from one individual. 



I. Five enucleated fragments were cut from eggs immediately 

 after they were released into the sterilized sea-water. These 

 fragments were kept in the water and then transferred into the 

 CaCla solution. After an hour's sojourn in this solution they 

 were put back to the sterilized w^ater, which was changed once. 

 ISlo asters appeared. 



