No. 2.] PLANOCERA INQUILINA. 199 
canals (wc). These unite to form the muscular egg-duct 
(Eiergang of Lang). This opens (at go Fig. 1) just behind 
the orifice of the penis, directly on the surface of the body, 
there being nothing which I can interpret as a bursa copulatrix. 
The numerous strands of the shell-gland (g/) converge from 
all points and open into the egg-duct. 
In several of my sectioned specimens I was struck with the 
great number of spermatozoa in all parts of the body. Lang 
(p. 638) has also found them in many Pseudocerids, not only 
in the oviducts but also in the gut-diverticula and in the 
parenchyma. In P. zxguzlina the short typically Planoceran 
spermatozoa occur, not only in the tissues of the gut, pharynx, 
etc., but even in the substance of the brain and larger nerve- 
trunks. There is undoubtedly in this species a true “hypo- 
dermic impregnation,” to use Professor Whitman’s term.! In 
the aquarium the sexually mature animals crawl over one 
another and thrust their stylet-shaped penes into one another’s 
bodies at any point. From this point, which may be found in 
sections, the spermatozoa travel through the tissues to the 
uteri. Spermatophores are not formed in P. zxguzlina as in 
leeches (vzde Whitman Z. c.) and some of the Polyclads (e.g. 
Leptoplana) described by Lang. 
As soon as the mature ova pass into the uteri a curious 
phenomenon, first seen by Selenka? in the uterine eggs of 
Thysanozoon Diesingit, may be observed. The wall of the 
germinal vesicle fades away and a spindle is formed with 
distinct polar suns containing centrosomes.? The small chro- 
mosomes, 9 or 10 in number, form an equatorial plate and 
appear to undergo fission, but of this Iam not certain. Then 
the polar asters grow faint and vanish and the nucleus returns 
to the resting stage during or just before oviposition. Before 
1C. O. Whitman, Spermatophores as a Means of Hypodermic Impregnation. 
Journ. of Morph., Vol. IV, No. 3, 1891. pp. 361-406. Pl. XIV. 
2 E. Selenka, Ueber eine eigentiimliche Art der Kernmetamorphose. Biol. 
Centralbl. 1. Bd. No. 16. 30. Nov. 1881, pp. 492-497. 
3 These last are pale and indistinct in P. zzgudlina, but in the Accelan Poly- 
cherus caudatus, Mark, they are remarkably large and distinct. This occurrence 
of true centrosomes in the mature but unfertilized egg is of interest from its bear- 
ing on Boveri’s well-known hypothesis. 
