Invertebrate Gallery of the Indian Museum. 45 



The Chastopoda are divided into two great natural 

 Orders, (i) the /'c/y^^.s'^^ or segmented Sea-worms and (2) 

 the Oligochasta or segmented Earth-worms. 



i. CH^TOPOBA POLYCH^TA. 



Good typical examples of Polychaetous Annelida are 

 the large Sea-worm, Eunice, from the Andaman Reefs, and 

 the species of Nereis from Norway, in Case 43. In Nereis 

 we find a distinct head (formed of two segments, — " pros- 

 tomium " and " peristomium"), provided with tentacles, 

 palps or feelers, and eyes. On the under (ventral) surface 

 of the head is the mouth, from which, in one of the speci- 

 mens of Nereis pelagica, the muscular pharynx with its 

 chitinous hooks and its pair of large sickle-shaped chitinous 

 jaws is seen protruded. 



Behind the head comes an indefinite number of equal 

 sized rings or segments, each of which bears, on each side, a 

 parapodium with dorsal and ventral cirri and bundles of 

 setae, while above the dorsal half-section of each parapodium 

 (notopodium) is abroad fiat membranous plate — the gill- 

 plate or branchia, by means of which the blood is aerated. 

 On the ventral surface of each segment are seen the depres- 

 sions where the excretory organs (" segmental organs"), 

 of which there is a pair in each segment, open. 



The last segment is smaller than any of the others, and 

 in the middle of it is seen the anus with a pair of long anal 

 cirri. 



The main facts of the internal organization of the typi- 

 cal Polychxta can be made out from the lettered dissec- 

 tions and sections of Eunice from the Andamans, exhibited 

 in Case 43. 



The bundles of setae, both ventral and dorsal, and the 

 gill-tufts which surmount the latter, are remarkably well 

 shown in the specimens of Chloeia. 



The Seaworms are sub-divided into two groups accord- 

 ing to their mode of life, namely the Errantia or free- 



