14 WORMS. 



We might inter that Nereis, possessing such a den- 

 tal apparatus, would be carniverous in its habits; but. 

 though it is very voracious, devouring other worms and 

 marine animals, it does not despise vegetable diet in 

 the form of marine alga:. Turnbull states that it is such 

 a greedy worm, " it will even devour its own immediate 

 relatives if hungry when it meets them : " and one worm, 

 confined by him in a small dish of water, bit itself en- 

 tirely through near the middle. 



The whole body of Nereis is covered with a thin, 

 tough cuticle like that of the earthworm, which may- 

 be removed without difficulty. The last segment bears 

 a pair of appendages, called cirri, and is perforated by 

 the anal opening. 



In this worm the sexes are distinct. During the breed- 

 ing season the eggs fill the body cavity, and pass out 

 through openings on the ventral surface which are diffi- 

 cult to detect. The eggs are found in masses, between 

 tide-marks, lying on the mud. 



The most important characteristic, and the one 

 which, at a glance, distinguishes Nereis from the earth- 

 worm, is the row of appendages which extends on 

 either side the whole length of the body. Every ring, 

 excepting the first two, may be seen to have a pair of 

 these appendages, which are called " paddles/' be- 

 cause, though they are used for respiration, they are 

 also locomotive organs. In order that their structure 

 may be more clearly seen, each pupil should cut out 

 one of the largest segments, and examine it with a 

 magnifier. 



Fig. 4 shows the paddles. -\m\ also the relative position 

 of the internal parts in one segment of the body. 



