88 LIFE BY THE SEASHORE. 



appears as a wide opening beneath an overhanging lobe, 

 and some little distance from the anterior end of the body. 

 In the second condition it appears at the end of the everted 

 proboscis, bounded by the great jaws, and opening directly 

 into the protruded pharynx, the proboscis itself being 

 merely the anterior part of the alimentary canal in an 

 everted condition. The actual appearance of the everted 

 proboscis with its small teeth is shown in Fig. 35. 



We may now pass on to consider the appearance of the 

 head proper. In the living animal, or in the dead animal 

 with retracted proboscis, the mouth is seen to be ventral 

 and overhung by the prostomium. On its dorsal surface 

 the prostomium bears two pairs of eyes, and in addition 

 a pair of very small tentacles and a pair of distinct large 

 processes called the palps (see Fig. 28). The next ring, 

 the peristomium, bears, as we have seen, no parapodia, but 

 only four pairs of long feelers or tentacular cirri, which are 

 used like the feelers of an insect. 



Behind this head region the segments are all uniform and 

 similar except the last, which is without parapodia, but 

 bears a single pair of long tactile cirri, or feelers. 



Having made out these points in the external anatomy of 

 a typical Chaetopod like Nereis, the next point is to get 

 some notion of the internal anatomy. This may be done 

 by proceeding at once to dissect Nereis; but unless some 

 experience has already been acquired, it will probably be 

 found easier to begin with the fisherman's lob- worm (Arenicola 

 piscatorum), which can readily be obtained of large size, 

 and which is exceedingly easy to dissect. 



The lob-worm is abundant on most sandy shores, especially 

 in sand which contains a considerable amount of organic 

 matter. It is a sedentary worm, burrowing in the sand, 

 and lining the burrow with an organic secretion, which 

 gives the walls a certain amount of firmness and renders 

 them easily visible when the sand is turned up. It swallows 

 the sand for the sake of its organic particles, and rejects 

 the indigestible residue in the form of the familiar sandy 

 "castings." If these be pushed away the mouth of the 

 burrow can be seen, and the burrow itself may be followed 

 some distance by digging in the sand. 



For the purpose of examination and dissection the lob- 



