434 



WORMS. 



SEA-MOUSE, Hermione hystrix (nat. size). 



(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 



\ \ / cod, haddock, and dog- 



fish. Another well- 

 marked family is that of 

 the Nereidce, in which 

 the predatory character, 

 coupled with ceaseless 

 activity, rapidity, and 

 sureness of movement 

 reaches its highest ex- 

 pression. The head of the 

 particular species (Nereis 

 incerta) represented in 

 the illustration shows 



two pairs of feelers (a and 6), as well as several pairs of longer organs of the same 

 nature (c), 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. 



Two more types of roving predatory worms are shown in the same illustra- 

 tion. Of these, Phyllodoce laminosa of the French and English coasts has as many 



HEAD OF Nereis incerta 

 (enlarged 4 times). 



