1022 ELLIOT ROWLAND DOWNING 
been considered that, perchance, some influence emanates from 
the central cell of a fortuitously accumulated mass as this cell 
divides, which, passed on to the adjacent cells, causes them to 
divide also. One is at a loss however to see why the influence 
should not be passed on to the still more peripheral cells so that 
all the cells of the gonad would divide more or less in unison. 
It is proper to speak of the division of these cells as synchronous 
only in a general way. It must not be taken to mean that each 
phase of division occurs in all simultaneously, merely that certain 
prophase and telophase conditions, that anyway last for a con- 
siderable time, are frequently found in all or nearly all cells of the 
group at once, so that the cells of the group in some stage of divi- 
sion, not necessarily exactly the same, will contrast with the sur- 
rounding tissue. 
One finds these synchronous cells more or less disconnected 
at times, as if the stress of the neighboring growing cells had 
broken the integrity of the mass. Still the general harmony of 
division is maintained, as would be the case if the blastomeres of 
a four- or eight-cell stage in a developing egg were separated by 
mechanical means. When this does occur the separated sperma- 
togonial blastomeres apparently proceed to form spermatophores 
of a fourth or an eighth the normal size, thus readily accounting 
for the previously noted variation in the size of the spermato- 
phores. 
THE SPERMATOPHORE THE GAMETOZOON 
It seems evident, then, that the development of the primary 
spermatogonia in the gonad, the same spermatogonia, when shed 
singly into the body cavity, and the giant spermatogonia are all 
in accord and are sufficiently suggestive of the development of 
the individual derived from the egg to make the hypothesis quite 
plausible at least that we have in Arenicola an alternation of 
generations. The primary spermatogonia are asexual spores, each 
of which, cleaving in a manner quite analogous to the cleavage of 
an egg, produces an individual, the spermatophore, all the cells 
of which are transformed into gametes. 
