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PACIFIC SCIENCE, Vol. VIII, July, 1954 
Fig. 2. Planocera pacifica, entire specimen. 1, Cerebral 
eyes; 2, tentacular eyes; 3, pharynx; 4, mouth; 5, male 
gonopore; 6, female gonopore; 20, brain; 21, tentacles; 
22, prostatic vesicle; 23, cirrus sac; 24, large teeth of 
cirrus sac; 25, uterine sac; 26, bulbous antrum; 27, 
cement glands. 
rectly behind it is seen the male copulatory 
apparatus, armed near the male gonopore with 
three large teeth. Behind this is seen the bulb- 
ous termination of the female copulatory ap- 
paratus. To either side of the male apparatus 
there occurs a sacciform enlargement of the 
uterus, presumably for the purpose of storing 
eggs. Such sacs are unusual in acotylean poly- 
clads. The details of the copulatory appara- 
tuses, insofar as they could be seen in the 
cleared whole specimen, are shown in Figure 
3^. 
For species discrimination, it was consid- 
ered necessary to remove the copulatory re- 
gion of the worm and section it sagittally. 
A view of the copulatory complexes as con- 
structed from the series of sagittal sections is 
given in Figure 3c. At the anterior end of the 
male apparatus is seen the elongated, curved 
seminal vesicle closely applied to the ventral 
wall of the prostatic vesicle. The common 
sperm duct enters the ventral surface of the 
seminal vesicle, passes slantingly and upward 
in the muscular wall of this vesicle, then turns 
back and becomes the lumen of the vesicle. It 
enters the proximal end of the cirrus sac in 
contact with the prostatic duct. The prostatic 
vesicle is a slightly oval sac situated at the 
anterior end of the cirrus sac but not bound 
with the latter in its muscular sheath. The 
prostatic vesicle has a thin muscular wall, and 
the interior is filled as usual with a much- 
folded, glandular eosinophilous lining. The 
short prostatic duct and the duct of the sem- 
inal vesicle enter the anterior end of the cirrus 
sac in contact with each other and terminate 
in the beginning of the ejaculatory duct. The 
cirrus sac is a large oval body with a thick 
muscular wall distally, a thinner wall prox- 
imally. This proximal half of the cirrus sac 
is filled with a loose tissue traversed by diag- 
onal muscle fibers and contains the slightly 
sinuous ejaculatory duct. This opens on a 
projection into what is presumably the lumen 
of the cirrus sac. This is widened anteriorly 
around the projection in question, then nar- 
rows to a tube running to the male gonopore. 
The lumen of the cirrus sac is lined by small 
teeth that increase in size distally. At the distal 
end of the cirrus lumen, where it opens into 
the male gonopore, are the three large teeth 
already mentioned. One of these and part of 
another appear in Figure 3c. 
The female gonopore occurs some distance 
behind the male pore and leads into an an- 
trum with excessively thick muscular walls, 
composed of circular and radiating fibers in- 
termingled. This muscular antrum, or bulbous 
vagina as it is termed by some, extends an- 
teriorly, gradually narrowing until it reaches 
nearly the level of the male gonopore. It then 
narrows abruptly into the vagina which turns 
first backward and then forward again, run- 
