SAND WORM. 



NEREIS VIRENS. 



THESE animals are found on the seashore in burrows of 

 sand and mud near low water mark. 



I. External Anatomy. 



1. General Features. Is there a differentiation into dorsal 

 and ventral? Anterior and posterior? How are these 

 regions distinguished? Compare w r ith the earthworm. 

 How many somites? Is the number as variable as in the 

 earthworm? Are the somites alike in size and form? Is 

 the body divided into regions? 



2. Head. In the head there are the following parts: 

 A triangular prostomium which bears on its anterior margin 

 a pair of short tentacles. On each side there is a fleshy 

 palp. The four eyes are on the dorsal surface of the pros- 

 tomium, and are sometimes hard to find. The peristomium 

 is the ring around the mouth. Compare it with the first 

 body somite. It bears four lateral or peristomial tentacles 

 on either side. Note the large jaws which may be partly 

 extended from the pharynx. 



Make a drawing showing the head and several of the 

 body somites. 



3. Appendages. On each side of most of the somites 

 there is an appendage called a parapodium. In each para- 

 podium there are the following parts: A dorsal blade, the 

 gill, which bears a short cirrus; and a ventral blade consist- 



