SEASONAL CYCLE IN PERCH SPERMARY 703 
cal points of the two curves. It cannot be positively affirmed 
from this evidence that changes in temperature are responsible 
for the initiation of certain processes in the testis, but it is 
significant that the tremendous synthesis of material which takes 
place in the testis is started in late August, i.e., in the period in 
which the temperature of the water surrounding the perch has 
reached its highest point and has begun to decline, and that the 
expulsion of spermatozoa takes place at the precise time in 
which the temperature of the water is beginning to rise. It has 
long been known at the University of Wisconsin that the date of 
the spawning of the cisco (Coregonus artedi) may be predicted 
rather accurately by following the temperature of the lake. 
During the fall of 1916 the temperature of the lake was a little 
higher than usual and numbers of ciscos were found by Mr. A. 
R. Cahn to be resorbing their eggs. It seems reasonable to 
presume that changes in temperature may influence the repro- 
ductive processes of the male perch when the reproductive proc- 
esses In the female cisco are dependent upon such delicate 
changes in temperature. 
SUMMARY 
1. A great seasonal variation exists in both volume and in the 
internal processes in the testis of the perch. The minimum size 
occurs from late June to late August. The maximum size is 
attained early in November. 
2. The testis is divided by connective-tissue partitions into 
lobules, but there are no seminiferous tubules. 
3. There is a cord of germ cells outside the body of the testis 
from which the testis is periodically supplied. 
4, An active migration of germ cells occurs from the cord, 
outside of the testis, to the ends of the lobules at the periphery 
of the testis. 
5. The lobules of the testis are gradually filled with an accu- 
mulation of germ cells. Transformation of the germ cells into 
spermatogonia and the process of spermatogenesis take place 
immediately after the accumulation has filled the lobules. 
