Worms. 



55 



of the back, marking the position of one of the main 

 blood-vessels ; the lower surface is lighter, often beautifully 

 iridescent. The body is composed of a large number of seg- 

 ments, the first and last of which are mocUfied to form the head 

 and tail respectively. As in the Crustaceans, each segment 

 bears a pair of locomotory appendages or feet, which, however, 

 are not jointed, each being provided with two bundles of bristles 

 and with a pair of little finger-shaped sensory organs, termed 

 cirri ; these feet are used for walking and swimming. Bristles 

 are absent from the head segment, but the cirri are enlarged 

 on that region, forming a number of sensory tentacles which, 

 in all probability, are put to the same use 

 as the feelers of insects and crustaceans. The 

 head also bears two pairs of small ej^es. A 

 pair of cirri are present on the tail. Nereis is 

 carnivorous, and when feeding, chiefl}? on 

 other annelids and crustaceans, protrudes a 

 muscular proboscis armed with strong jaws. 

 The sexes are separate, and the breeding 

 individuals undergo a peculiar seasonal trans- 

 formation, the eyes increasing in size and the 

 feet of the hinder part of the body acquiring 

 a paddle shape, modifications of structure 

 which go hand in hand with a marked change 

 in the habits, the worms in this condition 

 displaying an increased activity, swimming 

 great distances and often appearing at the 

 surface of the sea. Many species are found 

 in the same situations. N. pelagica is a little 

 smaller than N. cuUrifera, and reddish brown 

 in colour. 



Many common Polychsetes have the feet 

 permanently modified for swimming, the 

 cirri being transformed into leaf-like expansions, as in the 

 Paddle- worm (Phyllodoce lamelligera), which may attain a length 

 of two feet (Fig. 66). This is one of the most beautiful of our 

 littoral worms, the body being of an iridescent blue, with the 

 feet olive-green or brown. While the slender and elongate form 

 prevails in many of our marine Annelids, not a few of them are 

 less typically worm-hke. On hfting up stones at low water we 

 may often come across the little Polynoe squmnata (Fig, 67), 

 characterised by a very short and broad, much flattened body 

 an inch and a half long, with two rows of large, overlapping 

 scales, these scales being expansions of the feet, .Still less 



FIG. 67. POLYNOE 



SQ0AMATA (after 

 JOHNSTON). 



