VERMES THE WORMS 93 



termed the Heteronereis stage. In this form the Nereids 

 forsake their burrows, and swim freely in open sea. It is the 

 period of reproduction, but it must also add very consider- 

 ably to the death rate, for fishes are not averse even to 

 Heteronereis. 



Nereis is also viviparous. I have not seen the fact re- 

 corded, but quite recently, on dissecting specimens, I have 

 found fully developed young, an inch in length, within the 

 parent's body cavity. In this case the Nereis was in its 

 usual, not Hetero, form. 



Allied to Nereis are many other worms, some of very 

 great beauty. They are Syllis, Psammanthe, loida, etc. 

 Most of these are small, and live, mostly free swimming, 

 in open sea. Many are phosphorescent, and contribute in 

 a good measure to sea phosphorescence. Some have, be- 

 sides the usual sexual system, a reproduction by breakage. 

 In one species this has been carefully studied (Autolytus 

 prolifer). In this form, one of the central segments of the 

 body develops eyes, mouth, and antennse, then this portion 

 (the latter half) breaks off, and is a new individual, while the 

 anterior part proceeds to repair itself, to break off again. 



Nephtys margaretacea is cousin to Nereis. It is a large 

 and beautiful worm. As its specific name implies, it is 

 pearly white. It grows to a length of nearly a foot, and 

 lives in rather firm sand, from half-tide to low-tide level. 

 Under the name of " White Cat- worm " it is employed as 

 a bait by fishermen, but it is not so valuable for bait as 

 Nereis. Fishes in aquarium being fed with a mixed diet 

 would eagerly snap up Nereis and others, leaving Nephtys 

 to the last, and often neglecting it altogether. Nephtys 

 has. like Nereis and many others, a protrusible proboscis, 

 but it is not armed in the same strong manner, only a 

 ring of small conical teeth surrounding the mouth. 



The largest worm in the class is Marphysa sanguined, 

 the great rock- worm of the fisherman. 



