176 FLORENCE BUCHANAN. 



other associates are Nais littoralisj Hemitubifex (Clitel- 

 Ho) ater, nematodes, and planarians. It is, however, more of a 

 marine form than its associates, since, after heavy rain at low 

 water, it is, Mr. Shrubsole informs me, seldom to be found, while 

 the other forms of life may be still abundant. When present it 

 can, as a rule, be recognised readily by its nematode-like move- 

 ments and red coloui', and the four tentacles waving on its head. 

 It is usually from about 6 to 10 mm. in length, the size 

 varying according to the number of segments. It is, therefore, 

 slightly larger than the Haplobranchus. It forms loosely 

 coherent tubes by gathering up particles of mud round it, but 

 inhabits each only for a very short time. It is more frequently 

 to be found moving about in the mud. 



Anatomy. — The number of segments varies. I have 

 never counted more than forty-eight, and the greater number of 

 specimens examined had between thirty and forty. The body 

 is divided into regions which, as in other members of the 

 family, are not so distinctly marked off from one another as in 

 most sedentary annelids. 



Cephalic Region. — The 1st or head-segment has a 

 well-developed prostomium, on which are two well-marked 

 pairs of eye-spots, one pair more dorsal and median than the 

 other. In two out of the many specimens examined there 

 were eight eye-spots, not, however, arranged as four pairs, 

 but scattered and at very unequal distances apart. In another 

 specimen there Avere five eye-spots, three on one side and two 

 on the other. It is not unusual for the number of eyes to vary 

 individually in marine annelids; it is, indeed, usual for the 

 number to be greater in the larva than in the adult; and it would 

 therefore seem that the eight-eyed condition is to be explained 

 rather as a retention of a larval feature, than as due to the divi- 

 sion of the four eyes normally found in the adult. 



Behind the eye-spots, at the base of the prostomium, between 

 it and the body of the 1st segment, are the cephalic ten- 

 tacles, each containing a single contractile blindly-ending 

 vessel (PI. XXI, figs. 1 and 2, (.). They are richly ciliated 

 all round, the cilia not being confined, as in most other 



