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DR. H. W. HUBRECHT. 
it the second ciliated canal above mentioned opens, as 
indicated in the figure (PI. XXIII, fig. 6). 
Summarising the different phases in which this accessory 
apparatus to the brain is found in the various forms of 
Nemerteans, we have — a. A simple transverse furrow in the 
epiderm, on a level with the brain, which lies immediately 
under the epiderm. h. A slight complication of the furrow, 
and an external opening from which a short canal leads into 
the mass of nerve-cells from the brain (which in position and 
structure has undergone no change), c. A separation of 
the brain into three lobes, into the posterior one of which the 
ciliated canal, perforating the muscles and opening exteriorly, 
penetrates, whilst a mass of cells strongly resembling the 
cells of the wall of the oesophagus coalesces with this pos- 
terior lobe. At the same time we have sub. c, the three 
following modifications : — a. The external furrow as in 5, 
the internal canal simply bent. |3. The external opening 
modified into a deep longitudinal slit on both sides; the in- 
ternal canal either simply bent or divided into two. y. The 
external furrow as in h and ca\ the ciliated canal divides 
into two, one branch situated amidst the true ganglion cells, 
the other in the accessory mass of cells. 
As to the development of the apparatus, it has as yet only 
been studied in a few species. From the results arrived at 
by Metschnikoffj Leuckart, Pagenstecher, Biitschliy and 
Barrois, the author feels justified in concluding that — 1st. 
The exterior opening and ciliated canal leading amongst 
the ganglion cells of the brain are an invagination from the 
ectoderm. 2nd. The mass of larger cells (indicated by lighter 
shading in the figs.), in which sometimes a ciliated space 
persists, is an outgrowth from the oesophagus, afterwards 
separated from it ; by coalescence with the invagination of 
the ectoderm the internal space sometimes communicates 
with the exterior. 3rd. The bulk of the apparatus is directly 
derived from the brain, with which it remains in more or 
less intimate connection. 
The facts mentioned under the second heading would be a 
strong argument in favour of this apparatus having a respi- 
ratory function. The gills of Balonoglossus develop in the 
same way ; whereas here it is the blood fluid with* which 
similar outgrowths of the oesophagus become more intimately 
connected, it is in Nemerteans the heemoglobinous nerve- 
tissue. 
The author is not unwilling to recognise that in the 
higher differentiated Hoplonemertini the apparatus may 
gradually lose its significance as a special respiratory centre, 
