so 



PHYLUM ANNELIDA 



bears the following special sense organs : a pair of palps, large 

 cylindrical projections extending forward at its anterior end ; a 

 pair of tentacles, two delicate organs between the palps; and 

 two pairs of eyes, small, beadlike organs near the base of the 

 palps. Carefully identify all these organs and notice whether 

 the palps and tentacles are jointed. The metastomium is, in 

 Nereis, fused with the first two somites of the metasoma, or trunk, 

 and the segment thus formed is called the peristomium. It bears 

 the mouth and four pairs of long, flexible sense organs called the 

 peristomial cirri. Carefully observe, with the aid of a hand lens, 

 their exact position. These cirri are morphologically not cephalic 

 organs, as are the palps and the tentacles, but are remnants of 

 appendages of the first two somites. 



Exercise 1, Make an outline of the dorsal aspect of the head and the 

 first five or six somites on a scale of 5. Number the somites. Care- 

 fully label all the parts. 



Exercise 2, Draw a side view of the head on a scale of 5. Take special 

 care to represent accurately the position of the peristomial cirri. 



Exercise 3, Find a specimen, if possible, with the proboscis thrust 

 out and draw a dorsal view of its head. 



Note the tapering of the body at the hinder end. The worm 

 grows in length at this end. The posterior somites are the 

 youngest and hence the smallest. 



Exercise 4. Make a sketch of the hinder end of the animal. The long 

 sense organs at the extreme end are called caudal cirri. In which 

 direction do they project? 



The appendages in annelids are called parapodia. Carefully 

 examine the parapodia at different parts of the body and see if 

 they are all alike. 



Remove a parapodium from the middle of the body ; mount it 

 on a slide in water and study it with the aid of a hand lens or a 

 microscope. Compare it with the parapodia still on the animal 

 and determine which is its dorsal and which its ventral side. It 

 can be divided into two distinct portions, the dorsal and the 

 ventral portions, called the notopodium and the neuropodium, 

 respectively, each of which is stiffened by an internal, chitinous. 



