532 
HENRY LESLIE OSBORX 
of cytoplasm and as much of the cell is occupied by a large clear 
space, the cells have much the appearance of mucous cells. There 
seems to be no objection to identifying these cells as the prostate 
gland. 
The atrium (see fig. 3) has about the size of one of the ova. 
Its wall is different from that of the ductus in being less muscu- 
lar. It receives the uterus by opening on its right side. It is 
continued by a slender passage which runs obliquely in the space 
between the two ventral suckers to reach the genital pore. Its 
wall is equipped with a close layer of strong longitudinal fibres, 
no circular fibres can be seen and they seem to be absent. In 
order to exclude the possibility that one of the ventral suckers 
might be a part of the genital system, which possibility is sug- 
gested by the existence of genital suckers in some trematodes 
(as for instance that of Cladorchis, Fischoeder '03, fig. 80), a 
very careful examination of the exact relations of these terminal 
parts of the reproductive system was made, and all sections show 
with the utmost accord that the two ventral suckers are identical 
in structure and that neither one has any connection with the 
passages of the reproductive system. 
It has also been possible to demonstrate the entire independence 
of these parts by physiological evidence. In living specimens 
under observation it was possible to follow eggs in their course 
as they travel down the uterus toward the exterior. Such eggs 
pass close to the ventral surface then move up and around the 
posterior sucker, then down between the two suckers and finally 
emerge between them. 
There is a very great amount of difference among the trema- 
todes as to the details of anatomical structure of the outer organs 
of the genital system. In the most highly developed terminal 
or cirrus organ a sack encloses: an eversible cirrus or penis, an 
ejaculatory duct and a passage still deeper surrounded by the 
prostate gland cells and behind these the seminal vesicles. Such 
a cirrus organ is present in Clinostomum marginatum, an account 
of the anatomy of which is now in course of preparation by the 
writer. A less highly developed stage of organization is that found 
in Cotylaspis insignis (Osborn '04, fig. 35) where a strong mus- 
