SEASONAL CYCLE IN PERCH SPERMARY 693 
c. Clusters of germ cells occur at the periphery of the testis 
and their numbers are greatly increased at the time when the 
germ cells are found along the septum walls. Few mitotic 
figures occur, and it is evident that the original clusters of germ 
cells at the periphery do not give rise to all the cells found in 
this location a short time afterward. 
2. Germ cells along the septa between the lobules have an 
elongated and an irregular shape which suggests amoeboid 
motion (fig. 28). 
3. The germ cells in the region of the junction of the inter- 
lobular septa and the periphery of the testis (fig. 29) seem to 
show direct transitional stages between their migratory form and 
their resting form. 
During the migration there seems to be a slight increase in 
the volume of the cells. There is no change in the character 
of the cytoplasm, but the nucleus is a little more hyalin owing 
to the more even dispersion of the chromatin along the linin 
threads. 
After migration, the germ cells come to lodge at the distal 
end of the lobules. Some of the lobules do not extend entirely 
to the periphery of the testis, but end blindly a short distance 
from the center (fig. 2, c). In consequence, the germ cells, after 
their migration, occur in pockets some distance from as well as 
at the periphery. It seems that the tendency to migrate ceases 
only when the cells have definitely come into contact with an 
obstruction at the end of the lobule. This fact would seem to 
furnish evidence in favor of the germ cells accomplishing migra- 
tion actively rather than behaving in a purely passive manner. 
During the migration most of the cells are found along the in- 
side of the lobule, but some are actually within the intervening 
septa. Some recent work in tissue culture has shown that-in 
cells cultivated in vitro, migration is facilitated by the presence 
of strands along which the cells may move. The strands. of 
fibrous connective-tissue in the walls of the lobules would fur- 
nish admirable supports of this character. No mitotic figures 
- were observed in the migrating cells and it is assumed that they 
do not divide during this period. In this connection it is sig- 
