186 FLORENCE BUCHANAN. 



nally into two halves. Besides this there are in the anterior 

 region the three longitudinal chambers separated from one 

 another by the dorso-ventral muscles. 



There are nephridia of two kinds. In the anterior (tho- 

 racic) region of the body there are at once seen in the living 

 (fig. 1) two green tubes, one on either side of the alimentary 

 canal. On further examination each is seen to be bent on 

 itself, and cilia may be seen moving in it, especially well seen 

 at the bend of the tube which is in the posterior part of the 

 6th segment. As far as I can make out from examination of 

 the living and from sections, the opening to the exterior is 

 between the second and third ventral bristle bundles, in the 

 hinder part of the 2nd segment. By analogy we should expect 

 the internal opening to be in the septum dividing the 1st from 

 the 2nd segment. Whether this is so or not I am unable to 

 say ; I can trace the lumen of the internal limb in longitudinal 

 sections up into the 2nd segment to the level of the second 

 pair of bristle bundles, but it is difficult to trace further. It may 

 be that the septum is temporarily bent back, so as to lie partly 

 within the 2nd segment. In transverse sections the internal 

 limb (fig. 5, neph. i.) is not at all easy to see and to trace, since 

 it lies almost in the dorso-ventral muscles or is obscured by 

 them. The external limb (fig. 5, neph. e.) lies below the 

 internal one on either side of the ventral vessel, with it in the 

 middle one of the three longitudinal cavities shut off by the 

 dorso-ventral muscles. Both limbs consist of simple drain-pipe 

 cells. These nephridia are probably excretory in function.^ 



' Such thoracic nephridia in other sedentary annelids have been called 

 " tubiparous glands " by Claparcde and others ; but it is more probable, as 

 has been pointed out by Cosmovici, Soulier, and Bruuottc (as quoted by 

 Meyer in the ' Zool. Mith. v. Neapel ' for 1888), that it is the unicellular 

 glands of the epidermis, not the thoracic nephridia, which secrete the material 

 for fixing together the particles of mud or sand of which the tube is formed, 

 since worms from which the thoracic region of the body has been entirely 

 removed can still form tubes, and siuce the tube does not begin to be formed 

 until after the development of the unicellular glands. In favour of lliis view 

 is the fact tliat, in forms most nearly allied to the one we are here considering, 

 which are more tubicolous in habit, there are not these modified liioracic 

 nephridia. 



