NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 317 



necessary eventually to conclude that the relation between the 

 nucleoplasma ratio and the alternation of parthenogenesis and 

 sexual reproduction is not merely incidental, but that it does not 

 exist. 



It is not my purpose to discuss the possible physiological modus 

 operandi of changes of relative size of nucleus and cytosome. 

 That has been done repeatedly, in general terms, by others. 

 Some of the discussions of the general significance of this size 

 relation have already gone so far that it may now be desirable to 

 wait for the observed facts to overtake them. Certain of the 

 minor conclusions with regard to Hydatina may, however, prof- 

 itably be mentioned in their physiological relations. 



It is found that the nucleoplasma ratio of the yolk gland 

 increases during a series of generations. Had only the values of 

 K/P been obtained or studied, this might have been held to indi- 

 cate a reduction in the amount of cytoplasmic material produced 

 or at least of the contained yolk, while the nucleus remained 

 stationary in size or at least lagged behind the cytoplasm in a 

 decrease. However, the fact that the increase of K/P in the 

 yolk gland is entirely due to increase of the nucleus while the 

 volume of the cytosomal portion remains nearly stationary, 

 shows that an active nuclear change is involved. 



This increase of relative nuclear volume in the yolk gland 

 during a series of generations confirms the statements made for 

 Cladocera on which has been based the conclusion that the 

 increase is caused by long-continued parthenogenesis. The 

 stomach-intestine, however, changes only shghtly and in the 

 opposite direction. No change at all has been demonstrated in 

 the oocytes. It appears to be too early to generalize about the 

 effects of parthenogenesis on nuclear volume. 



There is also an increase in the value of K/P in the yolk gland 

 during the life of the individual. In this case, again, if only the 

 values of the ratio were known, it might be held that the increase 

 is due to a consumption of the cytoplasmic material or of the 

 contained yolk. It will be remembered that Lenssen ('98) was 

 of the opinion that the growing oocytes of Hydatina actually 

 ingest fragments of the yolk gland. The absolute measure- 



