SEASONAL CYCLE IN PERCH SPERMARY 691 
conforms to the shape of the cavity at the peripheral end of the 
lobule. In the pickerel the peripheral ends of the lobules be- 
come subdivided into pockets which are long and tubular. 
When the germ cells reach these pockets in the pickerel they 
become arranged along the inner walls, leaving a lumen in the 
center. Because of the peculiar form of these peripheral sub- 
divisions of the lobules and the relations of the germ cells to 
them, there is a resemblance between them and the seminiferous 
tubules of the higher vertebrates (fig. 23). 
There is a close resemblance between the cords of germ cells 
formed annually in the lobules of the testis of the adult perch 
and the formation of cords of primordial germ cells in the em- 
bryonic testis of mammals. In both cases the cord is formed by 
germ cells which have migrated into the testis from without. 
Here the resemblance ceases, for a part of the germ cells in the 
cord of the embryonic mammalian testis are destined to form 
nurse cells, while in the perch all the cells give rise to sexual 
products. 
There is a marked change in the somatic structures of the tes- 
tis during the changes in volume, but this does not involve 
growth. The interlobular walls become thin and the wall of the 
testis decreases in thickness. The blood-vessels dilate, appar- 
ently to meet the needs of the rapidly dividing germ cells. ‘There 
is no increase in the adipose tissue. The entire testis seems to 
be in a state of tension while it is at its maximum size, as evi- 
denced by the stretched condition of the interlobular and testis 
walls and by the deflection at the peripheral ends of the branches 
of the lobules (fig. 2, c). When the spermatozoa are expelled 
the region nearest the connective-tissue core on the ventral side 
of the testis is depleted first. When all the spermatozoa have 
been expelled, the normal thickness of the interlobular walls 
and of the testis walls is restored and the small size of the testis 
is resumed. 
It is interesting to speculate as to the character of the changes 
which occur in those teleosts which spawn but once in their 
lives. The Pacific salmon and the eel would furnish material 
for such an investigation. 
