68 A. C. OUDEMANS. 
sheath and behind the lower brain commissure with one 
another and with the median vessel, which in Tetrastemma 
never lies inthe proboscidian sheath. The two lateral 
vessels descend further between the lateral nerves and the 
cesophagus, and lie beneath the level of the nerve-stems, so that 
they are ventral, the nerve-stems already being situated ven- 
trally. The preparation was too imperfect to allow of the de- 
tection of transverse vessels. Perhaps they exist. 
20. Nemertes gracilis, Johnst. 
The specimen was cut sagittally, and about 23 mm. in 
length. 
In the hindmost part I distinctly saw transverse vessels 
running over the diverticula. They have no circular muscular 
fibres round the basal layer. 
The nephridial system is of unusual length, for in a specimen 
about 23 mm. long and 1 mm. wide I saw behind the ganglia 
one nephridial canal, and about 8 mm. from the tip of the 
snout two canals. Concerning their histological particulars I 
can make no definite statements. 
21. Malacobdella grossa (O. F. M.), Blainv., fig. 3. 
Tam unable to correct Von Kennel’s description, either of 
the vascular or of the nephridial system. I will merely give 
some additional observations. 
The cephalic loop runs over the proboscidian sheath, as in 
all other Nemertea. Not only from the two lateral vessels, 
but also from the cephalic loop numerous branches arise. In 
my specimen the median vessel had none. 
I could observe cilia, both in the two chief canals and in 
the excretory ducts of the nephridial system. The chief 
canals anteriorly lie above the nerve-trunks, then backwards ; 
they assume a more lateral position, and finally send the ex- 
cretory ducts with a little curve round above the nerve-stems ; 
they thus communicate ventrally with the exterior. 
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