ON THE BRITISH ANNELIDA. 22^ 



channel through which it is advancing. It requires little knowledge of the 

 composition of the sand of the sea-shore, saturated twice every twenty-four 

 hours by the tide, to understand that the food of these worms must share the 

 properties of the animal and the vegetable kind. The inferior forms of 

 life swarm in every minute mass of sand. The microscope detects thousands 

 of infusoria and entomostraca, and fragments of algaceous vegetables; 

 these organic substances constitute the food of these worms. The sand 

 swallowed " gives bulk," distends the canal, and sustains by mechanical con- 

 tact, the stimulus required for the due vermicular action of the tube. 



Clymene arenicoida displays a proboscis formed precisely on the same 

 model as that of Arenicola, and devoted to the same uses ; as this worm, like 

 Arenicola, lives on sand. The digestive system, however, is constructed 

 very differently from that of the latter. The oesophagus is short, the biliary 

 intestine begins near the head, and continues without any variety of struc- 

 ture to the tail. Neither the diverticular pouches of the oesophagus, nor 

 the gland-like flocculent vessels noticed in Arenicola, are detectible in this 

 species ; so that while the food and proboscis are identical, the digestive 

 system presents nothing in common in the two species. Another exemplifi- 

 cation is here given of the difficidty and danger of predicating the function 

 of an organ from the nature of its anatomical structure. 



The cognate genera of Amphinome, Chloe, Pleione, Euphrosyne, and 

 Hipponoe, far from common on the British coasts, in the pattern of the 

 alimentary canal, approach more or less intimately to the dorsibranchiate 

 type already described. 



The Euniciadcp. (Plate X. figs. 53, 54) are invariably armed with a power- 

 fully-jawed proboscis. It is capable of protrusion to a very slight degree beyond 

 the level of the mouth ; when fully extended it does not extend to the point of 

 the head. The jaws in all the species are very similarly formed and disposed 

 on the proboscis. Taking E. antennata for type, we observe that the jaws are 

 symmetrically bilateral, moved by strong muscles. The corneous processes 

 on either side of the proboscis, which constitute the jaws, are seen to con- 

 sist of two denticulated plates or saws, the teeth being directed inwards, of 

 a reaping-hook like piece, blacker in colour and stronger than the former, 

 and presenting a sharp edge; and another straight, tapering, and acutely 

 pointed piece, which in some species is situated to the outside of the former, 

 and in some to the inside. In such an engine the mechanician may recog- 

 nise the presence of the crushing, cutting, sawing, and piercing elements 

 artfully designed to do the multifold labour which the proboscis of these 

 rapacious worms is required to perform. In their native haunts they prowl 

 under stones, and closely resemble the Nereids in their habits, affecting simi- 

 lar situations. The oesophagus in this genus supports the tubular heart, and 

 presents the characters of an elongated gizzard. The intestine is brilliantly 

 yellow throughout the middle third of the body, and segmented by constric- 

 tions corresponding with those of the external body. The ultimate anatomy 

 of the biliary layer corresponds with those accounts of this organ already 

 given : it is densely vascular. Although the biliary gland commences in 

 front by an abrupt defined line, it very gradually disappears posteriorly, nor 

 entirely until it reaches the caudal extreme of the body. The anal orifice is 

 situated on the dorsal aspect of the tail, the latter being prolonged into two 

 long styles. It is a fact of fixed constancy in the organization of the Anne- 

 lida, that the outlet of the alimentary canal is situated dorsally whenever it 

 is not terminal. In the Serpulce, Amphitritce, Terebellce, it is terminal, the 

 mouth being also terminal. Whenever the anus is dorsally situated, the 

 mouth is ventrally placed ; these are fixed quantities in the organization of 

 the Annelids. 



