92 ANNELIDA. 



number 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 setse: (a) stiff and unjointed, (6) 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 Polychsetse. 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 

 seta?. Observe that the tunnel-like mouth is placed dorsally 

 and surrounded ventrally and laterally with flaring peristomial 

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

 these cirri represents the prostomium. 



2. The middle region consists of five somites. The first, 

 the eleventh segment, is marked by the great pair of wings 

 which are used to bring food to the mouth. Their dorsal sur- 



