3406 



THE WORM-LIKE ANIMALS 



SEA MOUSE, Hermione hystrix (natural size) . 



species these scales are concealed by a close felt of hairs, although in another kind 

 (Hermione hystrix), common in the Mediterranean, this coating of hairs is absent, 

 and the scales are exposed, as shown in the accompanying illustration. In spite 

 of their thick armature of spines, all the sea mice are greedily devoured by fish 



of various kinds, such as 



\ j \ / 1 1 c d> haddock, and dog- 



fish. Another well- 

 marked family is that of 

 the Nereidce, in which 

 the predatory character- 

 istic, coupled with cease- 

 less activity, rapidity, and 

 sureness of movement 

 reaches its highest ex- 

 pression. The head of 

 the particular species 

 {Nereis incerta) repre- 

 sented in the illustration 



shows two pairs of feelers {a and ) , as well as several pairs of longer organs of the 

 same nature (c) t situated at the sides of the head. On the thrust-out and upturned 

 proboscis may be noticed the two strong, sharp-toothed jaws (d) as well as several 

 smaller horny teeth (e). In the worm named Heter- 

 onereis, which is shown at A in the next illustration, 

 one of the chief peculiarities is that the segments in the 

 hinder half of the body are not so high as those in front, 

 and that they are furnished with far longer bristles, 

 whereas in Nereis all the segments are alike, being con- 

 structed on the same plan as those of the front half 

 of the body of Heteronereis. The exact nature of the 

 connection between these two marine worms does not 

 appear to be understood. The latter, however, seems to 

 be a stage in the development of the former; but not 

 an invariable stage, since adult examples of Nereis 

 produce young sometimes like themselves, and some- 

 times like Heteronereis. Allied to the Nereidce is Palolo 

 viridis, of the Samoa islands. Of this species Stair and 



Powell write that "every year the animal appears during October and November 

 in countless numbers at different spots on the coast; but the second swarm is even 

 greater than the first. . . . Both swarms seem to make their appearance on 

 the day before the last quarter of the moon, and on this day, but especially on the 

 day of the last quarter itself, the crowd of them is so inconceivably great that the 

 sea, even far from the shore, seems to consist of nothing else. The worms appear 

 with the dawn of light, and their number is at its height by sunrise, but after two 

 or three hours all have vanished." Curiously enough this mass of worms seems to 

 be composed entirely of living fragments, entire examples being never met with. 



HEAD OF Nereis incerta. 

 (Enlarged four times.) 



