98 



MR. E. C. BOUSriELD ON THE 



These organs are known as setae, their form being more or less 

 that shown in PI. TV. fig. 10 and PI. Y, fig. 16, curved like a 

 long /, with a central shoulder and bifurcate outer end. Eacli of 

 the bristle-bundles in the first four ventral pairs contains from four 

 to six such setae, 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 

 tw^o tapering bristles in a bundle, each of them is accompaniued 

 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 setae 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 Ophidonau'*," Journ. Linn. ^;oc'., Zool. vol. xix. p. 265, 1886- 



