THE SPERMATOPHORE IN ARENICOLA 1009 
parisons as they show the maximum gonad development. In 
September the blood vessel shows only a thin line of gonadial 
material in a very limited area. This grows rapidly from month 
to month until the gonad is of large size and is giving off spermat- 
ophores into the body cavity. Sections from the December and 
January worms show the maximum relative cross section of the 
gonad. It gradually decreases as its substance is given off into 
the body fluid as forming spermatophores during spring and early 
summer. During June the body cavity has its maximum of 
sperm. By the last of July and in August fibrous degeneration 
is evidently going on in the gonad (fig. 8-9), and the disintegrat- 
ing remnants of gonadial tissue are being ingested by abundant 
phagocytes (fig. 14). 
Though specimens of the other species have not been collected 
in such quantity as A. cristata throughout the year, yet enough 
of each has been seen to make quite certain that the description 
given will equally well apply to them, making allowance for the 
changed breeding period, always excepting A. ecaudata. 
By October the degenerative changes have ceased in A. cristata 
and multiplication of the gonad cells has begun again. A month 
before the gonad attains its maximum size the peripheral cells 
of the gonad are beginning to break away in small masses and 
float in the body fluid. The later development of these spermato- 
phores goes on in the body fluid. In October the margin of the 
gonad appears entire in section; in February and later the margin 
appears very ragged as the masses of gonad material are constantly 
discharging (compare figs. 7 and 8 and text figs. 1 and 2). 
EXTRA BLOOD VESSELS 
It will be seen then that the maximum size of the gonad does 
not coincide with the height of the breeding season. This is 
marked rather by the greatest abundance of the mature spermato- 
phores in the body fluid. In September the body fluid contains 
few or no sperm. By October they are appearing and steadily 
increase so that by November or December the fluid is crowded 
with the masses of developing sperm. An interesting develop- 
ment of the circulatory system goes on simultaneously with this 
