CHAECOPTERUS. 95 



in an aquarium for the habits. Notice the construction of the 

 tube and determine how it is formed. 



1. Notice the size of the body, also its gradual attenuation 

 posteriorly. Account for this condition. Observe how degen- 

 erate the parapodia are posteriorly from the same cause. 



2. The prostomium. Identify the tentacles. What is their 

 Dumber and arrangement? Find a pair of eyes dorsally 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 peristomium. What appendages does it carry? Note 

 the lower lip formed from the ventral edge of the peristomium. 



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 posi- 

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

 being represented only by the dorsal cirri and, toward the ante- 

 rior end, branchial cirri or gills. Acicula can be seen projecting 

 into the base of the dorsal cirrus. The neuropodium shows two 

 kinds of setae: (a) stiff and unjointed, (h) crochets. It also 

 bears an accessory cirrus and the ventral 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 Polychsetae. 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 l^e 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 

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



