TEREBBLLID^E. 95 



nephridial sacs in segments 10 — 13. The wide internal openings of the four fully- 

 developed organs are attached to the body- wall close behind the ventral " fascicles of 

 somites 5 — 8, and are overhung dor sally by a longitudinal lip furnished with a series of 

 small digitate processes ; lower down the anterior and posterior lips of the opening are 

 simple, thick-walled and ciliated. The aperture leads into a thin tube, which passes 

 inward and backward, curving round the inner end of the fascicle of bristles behind the 

 aperture, and then, crossing the continuous tube, passes up on the inner or mediad side 

 of the loop, at the apex of which it is continued into the efferent wider limb of the loop, 

 which passes down on the outer side to open into the longitudinal tube." He found 

 nephrostomes attached to the anterior faces of the septa behind segments 2 and 3, 

 but no external apertures in segments 3 and 4. Communications between suc- 

 cessive nephridia were found — the only case in Invertebrates — and Cunningham thinks 

 it approximates the condition of the nephridial system in Vertebrates. The gonads 

 are in the form of small, indifferent cells attached to the exterior of the seven nephro- 

 stomata, and are early shed into the ccelom, where they undergo further development 

 (Cunningham). 



The segmental organs in the Terebellids have a well-developed nephrostome — and a 

 longer or shorter U-shaped canal. The anterior organs with the opening of their funnels 

 in the diaphragms differ from the posterior, which have larger funnels and their ducts 

 lie in the nephridial mass (Hessle). Their variability was noticed by Meyer (1887), the 

 anterior differing from the posterior in the relative length of their canals. Whilst in 

 most genera the organs are free, they discharge into a longitudinal connecting duct 

 in Lanice and Loimia, and a similar arrangement occurs in Pista and in Lanicides. In 

 Amphitrite, whilst the anterior organs are free, the posterior lie very close to each other, 

 but no communication has been observed. Hessle (1917) utilises the nephridia in his 

 classification, but they do not seem to be of special service in this respect. 



Amongst interesting structural features in the Terebellids are the occurrence of 

 statocysts and statoliths near the cephalic ganglia in such as Amphitrite Edwardsi, for 

 example, and the presence of cardiac bodies in many. 



The genus Terebella was founded by Linnaeus for a series of red-blooded worms 

 sometimes embedded in sand, and at first forming a heterogeneous group from which 

 subsequent naturalists withdrew many species. In the twelfth edition of his c Sy sterna 

 Naturae' (1767), amongst other forms he inserted Terebella lapidaria, which had been 

 briefly described by Kahler, from Marseilles, in 1754. 



Savigny's (1820) first tribe of the Terebellidae under the general group of the 

 Serpulids was Terebella simplices, in which the upper lip was not dilated into two lobes, 

 the appendages of the first and third segments forming four lateral lobes directed 

 forward. Branchiae three pairs, ramified to the base and inserted on the second, third 

 and fourth segments. Ex. T. eonehilega, T. medusde, T. cirrata. 



His second tribe, T. Phyzelide, was characterised by having the superior lobe dilated 

 at the base in two tentaculiferous divisions. No appendages to the first and third 

 segments. Two pairs of branchiae ramified to the base and inserted on the second and 

 third segments. Ex. Terebella scylla, T. cincinnata. 



The third tribe was the T. Idalitf, in which there were no appendages to the first 



