98 
MR. E. C. BOUSFIELD ON THE 
These organs are known as set®, their form being more or less 
that shown in PI. IV. fig. 10 and PI. Y. fig. 16, curved like a 
long /, with a central shoulder and bifurcate outer end. Each of 
the bristle-bundles in the first four ventral pairs contains from four 
to six such set®, in length considerably exceeding those of the body 
generally, though there is but little difference in the general form. 
In the dorsal bristle-bundles, the first pair of which is found 
in the sixth segment, bristles of two forms are found. The 
first and most evident are tapering, projecting through the 
epidermis to a distance about equal to the diameter of the 
worm, and of these one is found in each bundle. The second 
are short, stout, notched at the outer extremity, and barely 
penetrate the skin. Notwithstanding their inferior length they 
are always the first developed, and if there should by chance be 
two tapering bristles in a bundle, each of them is accompanined 
by its own shorter one. 
The developmental relation between these two forms was 
pointed out by Perrier, and is additionally proved by the fact that 
in the posterior segments the tapering bristles are altogether 
wanting, the short ones alone remaining ; these at length are 
reduced to mere points in the last few segments, and finally 
disappear. 
Illustrations of the various forms of set® will be found in the 
figures already referred to. 
The integument of the worm is smooth, and shows but few 
palpocils, except at the head and tail, and even there not many ; 
they are connected with pyriform cells in the epidermis in the 
manner described by me in a previous paper*. 
The digestive canal conforms closely to the Naid type in its 
exsertile proboscis, its pharynx beset with mucous glands, and 
its long pharynx dilated at one point to form a gastric enlarge- 
ment, passing on into an intestine, capacious, closely beset with 
the so-called hepatic cells, and having a very strong inward 
ciliary current for a great part of its length. The segmental 
organs, which begin in the sixth segment, are essentially simple 
convoluted tubes with very narrow lumen, the dilated inner 
extremity being thickly clothed with fine short cilia. The 
external condition of these organs varies greatly. Frequently 
they are as described above, without any appendages. In other 
instances in the same species, at the same period of the year, 
* “ On Slavina and Ophidonais,” Journ. Linn. Soc., Zool. vol. xix. p. 265, 1886. 
