1012 ELLIOT ROWLAND DOWNING 
Gamble and Ashworth state (’00, p. 31) in regard to A. marina 
that ‘‘In large Arenicola, at certain seasons, the vascular process 
has no gonad and it is possible, as Cuenot (91) suggests, that a 
formation of the amoeboid corpuscles of the coelom takes place 
at this point when the animal is not breeding.” If this be true, 
evidently the gonad cells must form anew, as a proliferation of the 
peritoneal cells in adult life as well as in the embryological develop- 
ment and the distinction of germ cells and soma would be hypo- 
thetical. If so, too, the annual appearance of the germ cells must 
be due to a cyclical change in the organism contemporaneous with 
or due to the seasonal change without. Of course this must be 
true of their rapid increase anyway. 
I have examined many specimens of A. cristata taken in Sep- 
tember in which the body cavity showed no sperm, sectioning 
nephridia on whose blood vessel naked eye examination showed 
no gonad, but have always found under the microscope some gona- 
dial tissue. So that I feel reasonably certain that in this species 
at least, after once the primitive spermatogonia appear in the 
embryological development, they do not disappear. 
STRUCTURE OF THE GONAD 
These first few germ cells, then, formed from the peritoneal 
cells, multiply with rapidity until the entire gonadial vessel is 
covered with a thick incrustation of them. Division of the 
peripheral cells now becomes more rapid, so rapid in fact that the 
daughter cells do not grow to the size of the parent cells before 
‘division again ensues. There thus result zones of cells diminish- 
ing in size to the periphery of the gonad where they are being dis- 
charged into the body fluid. The largest cells, those adjacent to 
the blood vessel, are about 12. in diameter in A. cristata (11.674 
the average of over one hundred cells). The next smaller size are 
9.364 in diameter, then 7.55u and the outermost 6.024. In A. 
claparedii and A. grubii the cells adjacent to the blood vessel are 
smaller, only about 10u in diameter. 
Such an ideal arrangement of the cells is never found through- 
out the gonad. At some points the largest sized cells will at times 
