NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 313 



tion was attained, the absolute measurements of the nuclei in 

 both halves of the experiment have been collected and averaged, 

 with the following result : 



Mean area of intestinal nuclei in spring water 0.379 ± 0.00S7 



Mean area of intestinal nuclei in manure solution 0.391 ± 0.0088 



The nuclei are of practically the same size in both media, hence 

 the increase in relative nuclear volume in manure solution is 

 almost solely due to a decrease in the size of the cytoplasm. 



COMPARISON OF MALE-PRODUCERS AND FEM.\LE-PRODUCERS 



Female-producing and male-producing individuals from the 

 same famihes, reared under the same conditions, are compared, 

 with respect to relative nuclear volume, in table 9. Nothing in 

 the measurements indicates that the nuclei of one of these types 

 of female are significantly larger than those of the other type in 

 any of the tissues studied. The differences disclosed are not large 

 enough, relative to their probable errors, to prove a difference 

 between male- and female-producers. 



DISCUSSION 



The major result of the experiments described in this paper is 

 that no change of relative nuclear volume in oocytes, yolk gland 

 or stomach-intestine appears to have any relation to the type of 

 reproduction that occurs. This conclusion, while opposed to 

 certain phases of a widely held theory, is hardly a contradiction 

 of previously observed facts in any animal with alternating par- 

 thenogenesis and sexual reproduction. It must- be remembered 

 that the relation of changes in nuclear volume to cyclical phe- 

 nomena was first observed in Protozoa, and the idea was extended 

 to parthenogenetic animals at first on purely theoretical grounds. 

 Facts in support of that extension were later sought, but came 

 haltingl5^ Papanicolau's observations, described in the early 

 pages of this paper, were based on a very small number of indi- 

 viduals, showed differences that were mostly very slight, and were 

 in part contradictory to the theory. Hartmann's work was more 

 successful. Larger numbers of individuals were studied, and he 



