10 



THE OOCYTE 



lation medium. This isolation procedure was modified from the 

 technique of Hogeboom et at. ( 1952 ) for the isolation of mam- 

 malian cell fractions. I am indebted to Dr. Alfred Marshak for 

 his suggestion to use this medium in the isolation of oocyte nu- 

 cleoli. The nature of these preparations is indicated in Fig. 4. 



Chemical Froperties of Nucleoli. Some of the gross chemical 

 properties of the starfish nucleolus are given in Table I. 



Table I. Chemical Properties of Isolated Nucleoli 



" Vincent, 1952. 



* Baltus, 1954. 



" Present communication. 



<* Vincent, 1955a. 



' Vincent and Huxley, 1954. 



RNA Content of Nucleoli. The RNA concentration of nucleoli 

 from two species of starfish, Asterias forhesii and A. ruhens, ap- 

 pears to be about the same, averaging about 4% in each case. 

 Baltus ( 1954 ) found about 5 % RNA in sucrose isolated nucleoli 

 of A. ruhens where the author had found an average of 3.6% in 

 the same species when isolated in distilled water. As shown be- 

 low, no significant differences were found in the concentration 

 of RNA in A. forhesii nucleoli isolated in either distilled water or 

 the modified sucrose medium presented above. Changes of con- 

 centration and total content of RNA of individual A. ruhens nu- 

 cleoli during growth of the oocyte are presented in Figs. 2 and 3. 

 The base content of the RNA of nucleoli and cytoplasmic gran- 

 ules from A. ruhens is shown in Fig. 5 (data recalculated from 

 Vincent, 1952). Significant differences are found in both guanine 



