90 ANNELIDA. 



on the dorsal surface. They lead sluggish lives under stones 

 and are carnivorous. Note the size, color, and shape of the 

 worm. 



1. The elytra. How are they arranged? What purpose 

 do they serve? How many are there? With a hand-lens ob- 

 serve the fringed condition of the outer edge and the small 

 tubercles covering the surface. Note the color of the elytra 

 and the notches in the inner edges of the posterior pair. 



Remove with forceps all of the elytra on one side of the 

 specimen and the first two or three on the other side. Note the 

 stumps to which the elytra were joined. 



2. Examine the dorsal aspect of the head, and note the small 

 prostomium, with two pairs of eyes, three slender tentacles, 

 and a pair of fleshy palps. Outside the palps are two pairs of 

 cirri arising from the peristomium. The significance of these 

 will be understood later. 



3. Find the mouth, placed ventrally in the first or peris- 

 tomial somite. The mouth leads into a buccal region, which is 

 eversible and fringed at the end with papillae, each having a 

 dark spot at the base. If the pharynx is retracted, expose the 

 buccal cavity by a median ventral incision. In the anterior 

 end of the pharynx are four black chitinous jaws. Do you 

 infer that this species is carnivorous or herbivorous? The ever- 

 sible buccal region and the protrusible pharynx form the pro- 

 boscis. 



4. The anus is dorsally placed, and can be found beneath the 

 notches in the last pair of elytra. 



5. Examine the lateral appendage or parapodium of the 

 third or any subsequent somite. Note that it consists of a 

 stout ventral or neuropodial division, and a less prominent 

 dorsal or notopodial division, each supported internally by a 

 chitinous rod or aciculum, and bearing externally a tuft of 

 setae. If there is time, compare the form of the notopodial 

 and neuropodial setae. The typical parapodial structure is 

 completed by a soft neuropodial cirrus ventrally, and a noto- 



