SEASONAL CHANGES IN INTERSTITIAL CELLS 499 
son of the pictures side by side. To check this point the diame- 
ter of a large number of tubules were measured with a filar ocular 
micrometer with the results stated above. However, there is a 
great difference in the degree to which the tubules are filled 
with germinative cells. The open lumen seen during April and 
May is now filling up with spermatogonia. 
Cross and longitudinal sections of the testis rather indi- 
cate that the tubules are merely separated farther from each 
other when the interstitial cells are greatly developed. No data 
is available as to the length of the tubules. Reconstructions 
from serial sections would undoubtedly be necessary to Show what 
changes, if any, occur in this regard. There is no evidence of 
any atrophy of the tubules as a whole at this or any other 
period. The number of cross sections of tubules encountered in 
a complete cross section of the entire testis near the middle, 
just after the testis has been reduced in size, was about 850 
as compared with about 1000 when the testis is maximal in Size. 
In Six animals with testes at a minimum the number of times 
tubules were cut in a complete cross section varied from about 
750 to about 900 with an average of about 850; while in Six 
others with testes maximal in size the number varied from 900 
to 1100 with an average of about 1000. Since the testis enlarges 
from growth within, which undoubtedly increases the pressure, 
the testis is more nearly round at this time than when it is 
minimal. The transverse diameter is therefore relatively greater 
and this may explain this difference. On account of the Shape 
of the tubules these figures are probably of very little value. 
Since there is no sudden change in the tubules at the time 
when the testis rapidly diminishes in size, the decrease must be 
due to the atrophy of the interstitial cells, first in size and then 
more slowly in number. 
At no time was there any evidence of the crystalloids, first 
described by Reinke ('96) in the human testis as passing from the 
interstitial cells into the lymph vessels. While many subsequent 
writers have seen these crystals in the human testis, their 
passage into the lymph vessels has not been confirmed. It 
appears that these crystals have been found to any extent only 
