3432 



THE WORM-LIKE ANIMALS 



marine mollusks. In these, the body is short and broad and capable of but little 

 change in shape at its hinder end; it is furnished with a sucking apparatus, by 

 means of which the animal adheres to its host. As stated above, almost all 

 nemertines are of separate sexes; and in some marine species the development 

 of the young is so remarkable that it is impossible to pass it by without notice. 

 The young which issue from the egg are so unlike the parent, that no one would 



A NEMERTINE, Pterosoma planutn. 

 (Enlarged.) 



at first sight suppose them to belong to this group. The larva, as shown on p. 

 3433, bears some resemblance to a helmet, and has been named Pilidium. This 

 creature, which is covered with cilia, swims near the shore for sometime, while the 

 young nemertine is developed inside. As soon as this has acquired its cilia, and 

 attained a certain stage of maturity, it breaks from the pilidium and starts an 

 independent life. 



