DIOPATRA, CHAETOPTERUS 99 



placed behind the tentacles, also a pair of palps in front of 

 them. Note a second, larger pair of palps which serve as an 

 upper lip. 



3. The peristomiwn. What appendages does it carry? 

 Note the lower lip formed from the ventral edge of the per- 

 istomium. 



4. The position of the jaw apparatus can be identified as 

 being in a pouch ventral to the buccal region. Find both by 

 means of a probe. What kind of food are such jaws fitted 

 for? 



5. The parapodia vary greatly, depending upon their po- 

 sition on the body. Notice that the notopodia are vestigial, 

 being represented only by the dorsal cirri and, toward the 

 anterior end, branchial cirri or gills. Acicula can be seen 

 projecting into the base of the dorsal cirrus. The neuro- 

 podium shows two kinds of setae: (a) stiff and unjointed, 

 (6) crochets. It also bears an accessory cirrus and the ven- 

 tral cirri, which are curiously modified in most cases as glands 

 for use in tube building. Make out all these modifications 

 and where they occur. 



CHAETOPTERUS 



This is one of the most aberrant of our Polychaeta. It 

 lives on mud flats below low tide in a U-shaped, parchment- 

 like tube both ends of which protrude above the mud. In 

 the body three regions can be distinguished. Examine a tube 

 and see the size of its outer openings. Specimens may be 

 made to live in tubes of glass, bent to correspond to their 

 tubes, and their normal movements may thus be studied in 

 aquaria. What must be the source^ of the animal's food? 



1. The anterior region. Identify ten modified parapodia, 

 the fourth of which is supplied with a group of much stouter 

 setae. Observe that the tunnel-like mouth is placed dorsally 

 and surrounded ventrally and laterally with flaring peris- 

 tomial lips. Find the pair of peristomial cirri. The region 

 between these cirri represents the prostomium. 



