92 TEREBELLIDS. 



In the Terebellids, as in the Amphictenidas and Ampharetidse, the stomach and 

 intestine are surrounded by a blood-sinus, the ventral trunk receiving blood from the gills 

 and the alimentary blood-sinus. In some Terebellids, e. g. the Polycirrids, the gills are 

 absent and the blood is colourless or nearly so, but they have a circulatory system similar 

 to that of the Terebellids proper with a heart, but only a few cells to represent a heart- 

 body, and the current proceeds directly to the ventral trunk. Anteriorly the alimentary 

 canal has a tough investment with a few longitudinal and circular fibres, whilst a thick 

 coat of long gland-cells lines its interior, which is often thrown into numerous folds, two of 

 which ventrally are conspicuous and form indeed a kind of typhlosole. In most Terebellids 

 the stomach consists of two compartments, a muscular and a glandular cavity. The gut 

 posteriorly is loaded with sand-particles, sponge-spicules, diatoms, Foraminifera, 

 Radiolarians, and various organic structures amongst the mud. The coelom in autumn is 

 filled with the reproductive elements. 



Claparede 1 (1868) mentions that the dorsal vessel in Terebella multisetosa contains 

 a substance of a deep black colour distributed in irregular cords. In Terebella flexuosa 

 " the brown substance forms two lobed masses, one applied to the superior part of 

 the vessel, the other to the inferior. These two masses are not independent, but 

 united at intervals by thick connecting cords." He considered these bodies similar to the 

 chloragogenous tissue which surrounds the exterior of the ventral vessel, this tissue being 

 absent when the heart-body is present. He thought the Polycirrids were devoid of a 

 circulatory system. 



Cunningham 2 (1888) observes that in Amphitrite Johnstoni " the intestinal blood-sinus 

 is connected on the ventral side of the intestine with a large definite vessel, which at the 

 level of the posterior end of the heart divides into two branches : these pass up, one on 

 each side of the oesophagus, and unite to form the heart. Thus the paradox is here true 

 that the typical dorsal vessel is in these families (Terebellids, Amphictenidse and 

 Ampharetide) chiefly represented by a ventral vessel. The usual subintestinal or ventral 

 vessel is, of course, present in addition." 



In Amphitrite Johnstoni {figulusf the cardiac body " occupies nearly the whole cavity 

 of the heart, the channels left for the passage of the blood being very small. It is 

 composed of cylindrical cords which generally have a longitudinal direction, and they are 

 a mass of cells with large spherical nuclei which stain deeply. In Lanice conchilega the 

 body is proportionally smaller, the cords thinner, and confined to the immediate 

 neighbourhood of the walls of the vessel, so that a large central space is left for the 

 passage of the blood. In the cords a lumen is often, but not always visible. In Tere- 

 bellides stroemi only a single cord occurs in the dorsal vessel, and it runs longitudinally and 

 nearly fills up the cavity of the heart. The cord has a lumen with a radiate arrangement 

 of the cells." 



In Lepraea lapidaria (Fig. 148) the general arrangement of the cuticle, hypoderm 

 and muscular layers of the body- wall agrees with that in P. nebulosa, and the alimentary 

 canal is similarly slung dorsally, whilst inferiorly a double band of mesentery, apparently 



1 'Aimel. Chet. Nap./ p. 399. 



2 'Quart. Journ. Micr. Sci./ N.S., vol. xxviii, p. 261. 



3 Ibid., p. 264. 



