55 
testes ventrally, and during maturity the former may be inserted 
between the intestinal coeca. Neither kind occurs in any great 
numbers. Figure 1, Plate II a, shows the distribution of the ovaries 
in the body. The series of sections show that ovaries are absent 
in the prae-pharyngeal as well as the most posterior section of the 
body, and, as they are also lacking above and close to the pharynx 
and the main gut, they have become clustered in two more later¬ 
ally located longitudinal fields. They cease at quite a distance 
from the lateral margin of the body. Thus the female genital 
giands show a remarkable concentration, while that for the testes 
is even more marked. These, as a matter of faet, do not reach, 
neither rostrally nor caudally, as far as do the female giands. 
Moreover, as they are never compaetly arranged, we find here a 
modification in the sexual production uncommon in Polyclads. 
However, this reduction is not so extreme as that present in some 
minor Cotyleans from Antaretis: Enterogonimus, Stylochoides, Lep- 
toteredra, and especially Laidlawia, in which the ovaries through 
their production of large eggs have been considerably reduced in 
number. The same feature; i. e. a reduction in the number of 
ovaries due to the inerease in size of the eggs, also characterizes 
the exceedingly small Chromoplana and Åmyella from Japan (Bock, 
1922). In Euprosthiostomum, on the other hånd, the eggs are 
both relatively and absolutely rather below the average size 
and the ovaries small, and thus the reduction in the number 
of ovaries cannot be explained as in the above-mentioned species. 
The testes do not seem to have undergone any very distinet re¬ 
duction in number in the species enumerated above. 
The rnale apparatus agrees distinetly in its general characte- 
ristics with that typical for Prosthiostomum. Lang has given such 
an extensive and careful description of it in the case of Pr. siphun- 
culus that I shall merely deal with the differences present and refer 
to the text-figures 16 and 17 and Plate II a, Fig. 4. 
From the male genital pore, situated immediately back of the 
level of the insertion of the pharynx, the antrum masculinum runs 
in a backward-upward direction; in Pr. siphuneulus, on the other 
hånd, it goes forward-upward. Lang has considered that the latter 
direction argues in favour of self-fertilization, but this has, however, 
not yet been proved. The stylet of the penis of the species under 
