318 A. FRANKLIN SHULL 



ments of nucleus and cytosome show, however, that both nucleus 

 and cytosome increase up to middle age, the nucleus enlarging 

 somewhat the faster, while both of them decrease in size in later 

 life, the decrease of the nucleus lagging behind that of the cyto- 

 some. These facts suggest that in early adult hfe there may be 

 an active production of yolk material in which the nucleus 

 takes a leading role, but that in later life the nutritive processes 

 of the animal cannot keep up with the demands of the growing 

 oocytes for yolk so that there is an actual diminution of the size 

 of the yolk gland. The adjustment of the nucleus to the reduced 

 volume of the cytosome — a phenomenon observed in other cases 

 of reduction of cell size — would, whatever its cause, naturally 

 follow rather than precede the excess consumption of yolk 

 material. Such an explanation would not lead one to expect a 

 similar increase of the relative nuclear volume in other tissues, 

 and, as a matter of fact, there is httle or no change of tliis relative 

 volume in either the stomach-intestine or oocytes. 



Further need of caution against generalizing concerning the 

 nucleoplasma ratio in different tissues is shown by the fact that 

 manure solution causes an increase of K/P in the stomach- 

 intestine, but no change in the yolk glands nor, so far as can be 

 ascertained, in the oocytes. The nature of the effect, of the 

 medium on the cells of the stomach-intestine is problematical. 



Not the least valuable result obtained is the demonstration 

 that the nuclei of parthenogenetic and sexual females are of equal 

 relative size. It has lately been shown (Shull '21) that the 

 number of chromosomes is the same in both types of female, and 

 now it seems likely that these females are also equal in their 

 chromatin content. It had been suggested that a difference in 

 the quantity of chromatin might exist without involving a dif- 

 ference in chromosome number. 



SUMMARY 



1 None of the changes in the relative nuclear volume in the 

 stomach-intestine, yolk gland, or oocytes of Hydatina appear to 

 have any relation to the mode of reproduction, whether partheno- 

 genetic or sexual. Indi\ddual phenomena, if observed alone, 



