PRACTICAL DIRECTIONS 359 



Note : I. The head., consisting of (a) prostomium with its tentacles ', 

 palps, and eyes, and (b) peristomium with its tentacles ; also the proboscis, 

 month, and lateral chitinous jaws. 



2. The metameres of the body, each with a pair of (a] dorsal and 

 ventral cirri, and (b) lobed par apod s, subdivided into nctopod and 

 neuropod, each bearing a bundle of chitinous setcc. 



3. The anal segment with anal cirri, but no parapods. 



Carefully cut out an entire parapod and mount it on a slide (Fig. 

 88). Note the two bundles of seta, each made up of an aciculum 

 and of numerous jointed setoe of two different forms. The structure of 

 the setae will be more easily made out if separated from one another 

 with needles, or if the entire parapod is treated with a solution made 

 by dissolving 5 grammes of potassic hydrate in 100 c.c. of water. 



Prepare sections, in the usual way, of the prostomium, passing through 

 the eyes, and note the pigmented optic cup and retina, the pupil, and 

 lens, 



Procure some trochosphere larvae. Mount, and compare with Fig. 89. 



