492 ANDREW T. RASMUSSEN 



A comparison of the number of nuclei appearing in a cross 

 section of the entire testis before enlargement sets in, with 

 nearly twice the number of nuclei seen when these cells are at 

 their maximal development (i.e., when the testis is fully twice 

 its former diameter) indicates that there is an increase in the 

 number of interstitial cells at this time in the adult wood- 

 chuck. It is necessary to make the comparison in this way since 

 the testis, having doubled in diameter, will during the highly 

 developed stage give twice as many sections as when small. 

 If the cells have not changed in number, only half as many 

 nuclei will appear in a section of a given thickness in case of the 

 large testis as in the case of the small one, provided the nucleus 

 has not also changed in size, since the same number of nuclei 

 would in the enlarged testis be distributed in twice as many 

 sections. But in reality the nucleus has increased about 1.5 ix, 

 or 30 per cent, in diameter. While this is much less in propor- 

 tion to the increase (more than 100 per cent) in the diameter 

 of the whole testis, it is sufficient to call for some allowance. 

 By counting the number of nuclei in numerous groups of inter- 

 stitial cells resulting from the arrangement of the tubules in 

 the reduced testis, and comparing this with the number of nuclei 

 found in the same number of groups in the enlarged testis, it 

 appears that there are at least as many nuclei in a whole cross- 

 section of the hypertrophied testis as in a cross-section of the 

 testis before growth takes place. Making due allowance for the 

 increase in the size of the nucleus, the indications are that there 

 is a distinct increase in the interstitial cells of the hypertro- 

 phied testis. The assumption is that since there are as many 

 tubules intersected in the enlarged testis as in the small one 

 (as will be shown later in this paper), ther^- will be as many 

 cell groups confined between them. 



Further evidence also appears from the number of nuclei seen 

 in a section of the testis that has just undergone retrogression 

 such as will be described shortly. In such a testis the number 

 of nuclei appears to be distinctly greater than obtains in the 

 testis just before it enlarges (figs. 23 and 24). A larger num- 

 ber of animal at each stage with an actual count of the number 



