WORMS. 



229 



Fig. 224. — Head and jaws of 



titles, preforriiig, Iiowcver, to be near low water. ^Vi virens grows to a lenntli of 

 eighteen inclies or more. The color is dull bluish-green, with an iriileseeiit tiiiu'e of 

 red and other brilliant hues ; the large lamella; or gills along 

 the sides are greenish anteriorly, but further back often be- 

 come bright red, owing to the numerous blood-vessels which 

 they contain. It is a very active and voracious worm, terrible 

 to smaller animals, upon which it preys, capturing them by its 

 large pi'oboscis, which it suddenly thrusts out, seizing its vic- 

 tim with the two large jaws which arm the tip of its efficient 

 weajion of attack ; the proboscis is then 

 withdrawn, and the food torn and mas- 

 ticated at leisure. These lai-ge worms, 

 called " clam-worms " by the fishermen, 

 are frequently dug out of their burrows 

 and eagerly devoured by tautog, scup 

 and other fishes, — in nature it is ever 

 thus, the eaters are in the end themselves 



eaten. In JVei-eis the jiroboscidean armature emulates in strengtli 

 and sharpness the jaws of the ant-lion or some of the more 

 formidable carnivorous beetles; nearly all the free-swimming 

 Polycha'ta are similarly weaponed, and sometimes even more 

 formidably. Thus, in Phyllodoce- nmxlllosa, the fangs of a tiger 

 seem to have lieen conjoined with the cutting teeth of a shark, 

 to ]ierfect such a model of carnivorous dentition as can find no 

 rixal ill the animal creation. The JVereis does not always con- 

 tine itself to its l)urrow, but, like all its relatives, frequently goes 

 a-journeying. It is a nocturnal traveller, and at certain times 

 swims about in vast numbers near the surface of the ocean; 

 probably this habit has some connection with the reproduction. 

 The life history of Nereis is still very obscure, for in some cases 

 it j)roduces sexualh^ young which become Nereis ; in other cases 

 there intervenes what is known as the Ileteronereis stage ; Hetero- 

 tureis again is capable of reproduction, and api)arently the same 

 sjiecies may assume different forms; moreover Nereis is found 

 as a hermaphrodite as well as a unisexual animal. Now since the 

 connection of these forms with one another has not yet been satis- 

 factorily determined, the whole history of the manifold possil)le 

 changes is in confusion. 

 Verv different is it in regard to Autolytus, whose vital career, at least for the jires- 

 ent, is more comjirehensible. The genus may serve also as the type of the Syllidjs, 

 one of the chief families of the order, and remarkable for the great length of the 

 dorsal cirri of the body-sc'^mcnts. The eggs of Autohjlus produce an asexual indi- 

 vidual, which multiplies by division, the anterior end remaining the asexual worm, 

 while the ]iosterior individual is divided off and becomes male or female as the case 

 mav be. We have here a jmre example of alternation of generations, a phenomenon 

 first recognized about half a century ago. The individual born from the egg has 

 neither the form nor value — that is to say, the physiological significance — of a sexual 

 adult, but propagates itself by budding, division, or internal gemmation. Of tliis we 



