CIRCULATORY APPARATUS OF THE NEMERTEA. 39 
ducts of one pair, e.g., 277 and 305, or 361 and 366, which 
are removed twenty and twenty-four sections from one another ; 
and if we now know that sixty-six sections form 1 mm., then 
we see that these ducts were removed only between 3 and ¢ = 
= of a millimetre from one another. And we may conclude 
that such irregularities are the results of the high con- 
tractility of such worms as Nemerteans. If we reflect on 
all these causes, it is indeed striking how the ducts are 
arranged by pairs. 
The canals themselves in the transverse sections were very 
faintly coloured, and in the beginning I did not see them, not 
in any way thinking of a water-vascular system. (It was the 
first Nemertean I ever examined.) Already I had found and 
noticed more than one pair of ducts, and seen that they always 
began close to the inner longitudinal muscular coat, without 
comprehending their significance. It was Professor Hubrecht 
who not only drew my attention to the nephridial system, but 
who also decided as to the connection between these ducts and 
that system. When I had once observed this organ I saw it 
wherever it was present, and I immediately found even the 
smallest ducts of 4—6 mikrom. Shortly afterwards I could 
also very well see the connection of the ducts with the system 
of canals. 
The ducts have a wall of one single row of palissade-shaped 
cells, with granular contents placed side by side, somewhat 
obliquely bent outwards. Each cell is provided with a cilium 
of up to 200 mikrom. in length. It may be remarked that the 
excretory ducts are all open towards the basal membrane, then 
suddenly narrow, as if the basal membrane contracts them. 
Outside the basal membrane they widen again, but here I rarely 
saw their lumen. Where it was visible I again saw large 
cilia, and the cells were still more granular, and their limits 
were not sharply visible and they were not so well coloured as 
the cells of the duct within the basal membrane. Although I 
saw distinctly in Carineila and Carinoma that the basal 
membrane was pressed outwards, in Valencinia longirostris 
I saw neither this nor the reverse. The basal membrane was 
