ON THE BRITISH ANNELIDA. 231 



conformations. This, however, is only true with reference to adult indivi- 

 duals, since it is easy to assign to distinct species individuals which really 

 differ only in age, and that on the ground of an apparent difference in the 

 form and shape of the proboscidean jaws. 



The Nereids (figs. 55, 56, 57, 58) swallow a considerable amount of clay 

 and sand. Observation of the habits and habitats strongly suggest, however, 

 their carnivorous disposition. The proboscis is well- constructed, and the jawa 

 aptly disposed, for seizing a living prey. The intestine is filled always, espe- 

 cially throughout the posterior half of the body, with a pulpy matter, of which 

 sand and clay form a large proportion. These worms frequent subterranean 

 channels constructed by themselves ; and this mechanical purpose is not the 

 least important of the uses to which their proboscides are devoted. Through 

 these haunts they move with great rapidity. They prowl on all animals which 

 perchance may be brought within the precincts of their territory by the 

 mechanical force of the tidal currents. 



As the British species in the genus Nereis amount to a considerable num- 

 ber, it were tedious in this place to enumerate all the specific variations from 

 the generic type which are found to occur in the figures of the proboscidean 

 jaws (figs. 55, 56, 57, 58). In the definition of species, these particulars may 

 hereafter prove of essential service. 



Assuming for type this organ as it occurs in Nereis margaritacea (fig. 55), 

 it is found to be capable of extrusion to some distance beyond the line of the 

 head; that the jaws are two in number, one on each side of the terminal 

 orifice of the proboscis ; that each jaw consists of a falcate, horny, dark pro- 

 cess, the internal curved edge of which is irregularly notched : the cha- 

 racters of these notches become distinctive of species. In some they are 

 uniformly round ; in others they are sharp and recurved ; in others these 

 serrations point forwards. This latter is the case in more than one of the 

 smaller species. It is important to remember that in no species of this genus 

 do the jaws exceed 'i\ie pair ' in number. In addition to the jaws, properly 

 so called, the proboscis in some species is pricked with minute corneous 

 points at various parts of its surface, for the purposes obviously of protec- 

 tion from external injury. In N. margaritacea the oesophagus extends back- 

 wards to the level of the seventh or eighth foot ; it is a straight muscular 

 tube as usual; but it is curious to observe that the two lateral pouches 

 communicating with the oesophagus already described in Arenicola, re-appear 

 in the genus Nereis. They are obviously identical in structure to those of 

 Arenicola, and subservient to similar purposes. At the distance of three or 

 four feet beyond the point of these pouches the biliary intestine begins. It 

 is strongly segmented. In the smaller species the interval of constriction 

 equals in length the sacculated portion. The only means of distinguishing 

 between the limits of the true ' digestive ' intestine and the colonic, consist 

 in the character of their respective contents ; true faecal matter never lodges 

 in the former, it always accumulates in the latter. In those Annelida, as the 

 Nerine, for ejcample, which are remarkable for the elongation of the body, 

 the posterior half or third of the intestinal canal is loaded with fseculent 

 accumulations, imparting their colour to the whole body. The system of 

 the blood-proper, as formerly indicated, is elaborately developed in the Ne- 

 reids, and the walls of the digestive canal are embraced by a dense tissue of 

 a closely reticulated plexus. In the Nereids, the integumentary structures 

 are far more vascular than those of any other known Annelid. This circum- 

 stance suffices to account for their proverbial muscular activity. The evi- 

 dences of structure and habits concur to support the view which assigns to 

 these worms an almost exclusively carnivorous character. 



