1036 ELLIOT ROWLAND DOWNING 
some time in its life history cells are developed within its central 
cavity—the primitive germ cells or spore mother cells. These 
develop spores which we know as spermatogonia or oogonia. Such 
spores, in Volvox, develop new ¢olonies which may be sex- 
ual and which are freed when the parent disintegrates. In the 
Dicyemidae, if a gametic individual develop from such spores 
(or Keimzellen) it is retained in the parent where it disintegrates 
to free its egg or sperm. In a word the gametozoon degenerates 
prematurely within the sporozoon. Now in Arenicola, I take 
it, the development of the spermatogonia into the spermatophores 
is the development of the gametozoa. Gametozoon degeneration 
begins before its development is complete and the sperm are pro- 
duced by a short cut. Instead of developing an individual, with- 
in which some cells form the clusters of sperm, its cells form the 
sperm cluster immediately. In this genus, as I have already 
shown is the case in Hydra, the sperm seems to form within the 
spermatid, reminiscent perhaps of the primitive condition found 
in Volvox of forming the sperm within the cell. 
For the sake of my theory, I should like to agree with Tann- 
reuther in the spermatogenesis of Hydra. He claims that the 
spermatozoa develop ‘in groups, each group enclosed within a 
single cell or cyst. But the clearness of my own preparations 
seems to negative completely such an interpretation. I can only 
reiterate what I have already published on the spermatogenesis 
of this form. It is too bad, for Hydra would make even a better 
transition form than it does, between such a spermatogenesis 
as we have in Volvox and the typical animal spermatogenesis 
in which the spermatid transforms into the sperm in its entirety 
rather than developing the sperm within it. 
Hartmann, in the paper on the Dicyemids, describes briefly 
and figures a development of the fertilized egg that is very similar 
to the development of the asexual spores. The same parallelism 
is noted in many botanic papers, the oospore developing much 
as an asexual spore does in its early stages. To find, then, in 
Arenicola that the spermatogonia or asexual spores develop to 
produce the spermatophore or gametozoon in a manner homol- 
ogous to the development of the fertilized egg is to strengthen the 
position taken that the spermatophore is the gametozoon. 
