170 WHEELER. [VoL ix: 
vation.” That Syxcelidium cannot be the young of B. can- 
dida is at once apparent from the fact that the former species, 
when fully grown and sexually mature, is considerably smaller 
than the latter species at the time of hatching ! 
The appearance of S. pellucidum, when resting fully extended 
on a dark background, is reproduced in Fig. 2 under a low 
magnification. In the middle the sides of the body are 
parallel, but towards either end they converge uniformly. The, 
intestine shows through the pellucid body-wall as a flesh- 
colored mass. Anteriorly the brain is easily seen as a pair 
of transparent swellings, which form haloes around the two 
black eyes. Other structures which may be seen with a low 
power are the pharynx, penis, and the two rosette-like uteri. 
Like the species of Bdelloura, S. pellucidum is very active 
in its movements, creeping with a steady, rapid motion over 
smooth surfaces, or swimming at the surface of the water after 
the manner of the fresh-water Triclads and Pulmonate Mol- 
lusca. Rapid movement appears to be very common in the 
marine Triclads; Lang (81°) mentions it in his description 
of Gunda segmentata, and I have observed it in a pretty little 
Fovia which occurs sparingly under the stones between tides 
at Wood’s Holl, but which my friend, Dr. E. O. Jordan, 
collected for me in great numbers on Monhegan Island, Me. 
Syncelidium occurs only between the leaves of the gill- 
books of the Lzwaulus, never migrating to the bases of the 
cephalothoracic legs like the young and sexually immature 
Bdelloure. 
THE ANATOMY OF SYNCCLIDIUM. 
1. Lutegument. 
The rather dense cilia covering the whole body are some- 
what longer on the ventral than on the dorsal surface (Fig. 
10); measuring on the former .4 p, on the latter .2 4 —.3 pb. 
They are borne by a compact membrane (zg) which stains 
quite deeply in the various carmines. In cross-section it 
appears to be homogeneous and somewhat thicker on the ven- 
tral (.3 ») than on the dorsal surface (.25 #). No nuclei could 
be detected in this membrane, but when the planarian was dried 
