Relation between Nucleolus and Chromosomes. ^5 



main processes, but a slight variation in details, together with a non-corre- 

 spondence in the time of occurrence of the successive stages. 



On the question of the individuality of the chromosomes Hipponoe yields 

 no positive results. Even in the late growth-period there is no indication 

 of chromosomes as such. And it is clear that at least a large part of their 

 chromatin is either contributed by the disappearing nucleoli or elaborated 

 by the cell protoplasm. Hipponoe supports the conclusions drawn in regard 

 to the function of the nucleolus in the case of Asterias, that it serves in part 

 at least as a storehouse of nutritive material contributed to the chromosomes 

 prior to maturation. 



SUMMARY OF RESULTS ON ASTERIAS FORBESII. 



1. Synizesis occurs in the oocyte of the first order at the very begin- 

 ning of the growth-period (size of nucleus 5 microns). 



2. The growth-period is passed through rapidly. The single spireme of 

 the contraction phase becomes double and segments into a number (18?) of 

 irregularly shaped chromosomes. These decrease in size and collect in one 

 or several masses of minute bilobed bodies in close proximity to or upon 

 the nucleolus. 



3. During the latter half of the growth-period all the chromatin, with the 

 exception of what is held by the chromosomes, becomes stored in the en- 

 larging nucleolus, the linin mesh work of the nucleus being left entirely 

 achromatic shortly prior to maturation. 



4. The nucleolus consists of a plastin ground-substance infiltrated and 

 covered over with chromatin. In the living condition of the oocyte the 

 nucleolus appears vacuolated. The " vacuoles " are spherules of fluid chro- 

 matin, and where these are filled, properly stained sections reveal a homo- 

 geneous structure of the nucleolus. Linin, plastin ground-substance, and 

 chromatin appear to represent closely related substances, possibly different 

 phases of elaboration of the same fundamental material. 



5. The chromosomes do not arise out of the nucleolus. The latter con- 

 tributes nutritive substance to them, by virtue of which they increase slightly 

 in size before entering the first maturation spindle. 



6. The number of chromosomes in the prophase of the first polar mitosis 

 is 1 8. They vary somewhat in size (one is considerably larger than the 

 rest), all have a characteristic dumb-bell-shaped appearance, and some are 

 clearly double (bivalent). 



7. The two maturation divisions effect a double longitudinal fission of the 

 original bilobed chromosomes. The reduced number of chromosomes is 

 again 18. 



8. Observations on Hipponoe esculenta agree in essential points with 

 those made on Asterias forbesii and support the conclusions regarding the 

 origin of the chromosomes, the function of the nucleolus, and the reduc- 

 tion phenomena. 



