WORMS. 153 



138. The young come from eggs as free-swimming ani- 

 mals, furnished with eyes and jointed appendages provided 

 with hairs. In this condition they swim about for a while, 

 and then acquire a bivalve shell, and in this state remotely 

 resemble the little creatures shown in Fig. 138. 



In Fig. 141, .the letter^, represents its first appearance 

 from the egg. Its next appearance with the bivalve shell is 

 shown at B. After remaining a free-swimming animal for a 

 while it becomes attached to the rock, adhering by means of 

 appendages on the head, and, then moulting, it loses its former 

 appearance ; the appendages change their proportions, new 

 parts are added, the eyes disappear, a limy shell gradually 

 forms around it, and it assumes characters entirely unlike 

 those of its earlier stages. 



CHAPTEK XX. 



WORMS. 



139. AMONG the animals thus far studied, having a body 

 composed of segments, the pupils have seen that in all cases 

 the appendages were jointed, that is, the legs and antennae 

 were composed of distinct segments or joints ; and, with the 

 exception of the myriapods, or centipedes, the animals pos- 

 sessed a limited number of segments to the body. 



In the group of animals now to be studied the worms 

 the body has, generally speaking, an indefinite number of 

 segments, and there are no jointed appendages attached to it. 



