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A. FRANKLIN SHULL 



old females, is four times its probable error, and appears certainly 

 significant. 



Changes in the size of the cytosome in the yolk gland are also 

 shown by the measurements made. Since the yolk gland is a 

 syncytium, the cytosome of single 'cells' can be measured only 

 when the section passes through but one nucleus. Safe compari- 

 sons can be made so long as sections of approximately the same 

 size are used. Probablj^ the most satisfactory criterion of size, 

 for this purpose, is the number of nuclei cut in the section, since 

 the nuclear content of the section would be much less variable 

 with this criterion than with the criterion of equal absolute area 

 of the figure. Sections containing two nuclei are, on the whole, 



TABLE 7 

 Mean absolute sizes of nuclei in yolk gland of Hydatina senta females of different 

 ages, expressed in square inches on drawings. Also size of cytosomal portion of 

 gland, as shown by sections containing two nuclei 



more numerous in my material than any other size, and these 

 alone are used in the comparison. The areas of the cytosomal 

 part of these sections are added to table 7, in the last two columns. 

 The figures show that the cytoplasm is more abundant at middle 

 age than earlier, but is later reduced to an amount less than that 

 in the young adults. 



From the data given in table 7, therefore, it must be concluded 

 that the rather steady increase of the relative nuclear volume of 

 the yolk gland during the lifetime of an individual is accomplished 

 in the following manner. The increase from early adult life to 

 middle age is the result of absolute increases in both nuclear and 

 cytosomal volume, the percentage of nuclear increase being much 

 the greater. The increase of relative nuclear volume from middle 



