natural scavengers, have a powerful sense of smell, and had probably 

 scented the fish a long way off. These mollusks seemed to be able to 

 live as well out of the water as in it. 



Reaching the shore, we ate our dinner, and then returned to the 

 station by a route which took us across a salt marsh, in which we found 

 a large number of the amphibious snail Melampm,' which always lives in 

 the vicinity of the sea. A large mussel, Modiola plicatula, was found 

 here in great abundance. 



About the middle of the afternoon, we took the train for Providence, 

 and settling back in the comfortable seats, plied Professor Parker with 

 questions. George wanted to know how the shells grew, and if the 

 young animal was like the old one. " No," replied the Professor, " the 

 young are quite different. After leaving the 

 egg, the young mollusk, which is very small, 

 is called a veliger larva, and swims about by 

 means of two lobes, or vela, which are placed 

 on each side of the animal and are covered 

 with hairs, or cilia, by the rapid motion of 

 which the larva swims about. All mollusks 

 are free and active when young, and spend a 

 greater or lesser time in swimming about. As 

 the organs become more developed, the vela 

 gradually disappear, the head, foot, tentacles, 

 heart, and other organs are formed, and the 

 young mollusk sinks to the bottom of the sea, and takes up its adult 

 condition. If an attached species, it fastens itself to some object; if a 

 free-moving snail, it selects some rocky or sandy spot for its home. You 

 will observe from this rough sketch which I have made, that the young 

 mollusk is as different from the adult animal as the caterpillar is from 

 the butterfly." 



We arrived home at supper-time, tired in body, and as Harry ex- 

 pressed it, " as hungry as wolves." 



Veliger larva, or young of 

 Rissoa costata, a minute gastro- 

 pod. The vela or ciliated lobes 

 are seen on each side of the 

 animal, and the eyes, foot, and 

 tentacles are seen in the center. 

 (Tryon.) 



93 



