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uterus itself communicates with the exterior by the same open 
cavity or pore as does the penis. This pore is much larger and 
more important in the Dendrocoels than in Opistomum and 
its allies. The exact anatomy of the uterus and its connected 
glands is still doubtful, according to Mecznikow, although most 
carefully investigated by Schultze. The reader, perhaps, may 
be induced to try to place it beyond a doubt. 
We pass on now to Polycelis. It is to this genus of the Plana- 
rians with tree-like intestines, that our common little black 
Planaria ( Polycelis nigra) belongs ; other dark-brown and 
blackish species are not uncommon about the same size or a 
little larger (to the third of an inch), and belong, some to the 
genus Planaria , some to the genus Polycelis as defined above, 
and are distinguished to a great extent by the shape of their 
frontlets. Some species (PI. lactea, &c.) are to be got which 
are quite white and clear, and are admirably adapted for study. 
The same ciliation of the surface, and the same, though more 
elaborate, corpuscles in the skin, are to be noticed in Polycelis 
as in Opistomum. The subcutaneous muscular system has 
even a more extraordinary development, for the animals flow 
or slip over a surface more like a liquid drop on a piece of glass 
than living creatures. The mouth (fig. 12) in our figure of the 
digestive organs of Planaria lactea is, as in Polycelis, near the 
centre, and leads into a large, exsertile, suctorial pharynx ; this, 
according to the observations of Duges, the animal protrudes, 
and firmly fixes to small worms, insects, larvae, or whatever may 
be its prey, and through it sucks their juices. The beautifully 
dendroid character of the intestine is well seen in the figure. 
The nervous system, which in fig. 10 is illustrated by that of 
Polycelis cornuta , is similar to that of Ehabdocoels, but its 
branches are more obvious. The water- vascular stems are 
obscure, but Max Schultze says he has seen them in PI. torva , 
and so we may expect them in Polycelis. The generative 
organs are highly developed in Polycelis and its allies. In 
fig. 21, the penis, uterus, and ends of the sperm-ducts of Poly- 
celis nigra are drawn. The penis is covered with spines, and 
varies curiously in shape in different forms. In fig. 11, the 
genitalia and pharynx of Planaria torva are drawn according 
to Schultze. Polycelis differs from this only in one important 
matter, and that is the absence of the little gland or sup- 
posed spermatophore ( h ). As in Ehabdocoels, we have vitel- 
laria, ovaries, and a uterus, spermatheca, testes, seminal vesi- 
cles, and a penis, as also a very large cavity or vestibule 
into which they all open. Oscar Schmidt has written some very 
beautiful papers on these organs in Planaria and Polycelis 
(Zeitsch. fur Wiss. Zool. bd. x. xi.), and has shown how 
their arrangement differs in different species. 
