298 



A. IZUKA. 



At ebb-tide, the worms are found burrowing in the mud or sand to a 

 depth of a foot or more. In the burrows they move about sluggishly at 

 the most. The entrance into the burrow is usually indicated by a small 

 round hole on the bottom surface. With the flood tide, irrespective of 

 the hour of day, they leave their retirement and creep about on the 

 bottom. They are then very active and voracious, feeding on various 

 aquatic animals and plants. When disturbed they take to swimming. 

 This they do actively, progressing head foremost, by a wave-like move- 

 ment of the body, which movement starts at the tail and proceeds towards 

 the head. 



Scince we have to do with immature growing worms, it is but natural 

 that the dimensions are exceedingly variable ; but it may in general be 

 said that they show a length of 60-100 mm. and a breadth of 5-6 mm. 

 The number of segments varies of course according to the size of 

 individuals ; in a large one there may be as many as 120 segments. 



When alive the body is translucents and generally of a pinkish yellow 

 colour. The gut and blood vessels show themselves plainly through 

 the body wall. The colour of body differs much in shade according to 

 whether the gut is full or empty. The two brown bands exist on the 

 anterior segments but are not at all so conspicuous as in European 

 specimens of Nereis divcrsicolor. In the specimens preserved in alcohol, 

 the colouring matter has dissolved away, leaving only a light brown hue 

 on the anterior dorsal surface of the body. 



Mature worms. — In this annelid there is no marked structural 

 difference between the immature and the mature, or terminal pelagic stage 

 except in colour and dimensions. The colour changes with the develop- 

 ment of sexual products ; it again differs according to whether these are 

 eggs or spermatozoa. The sexual products which fills up not only the 

 body cavity proper, but also its extension into the parapodium greatly 

 distend the body wall ; so that fully mature worms generally attain a 

 length of 1 10-120 mm. and a breadth of 7-8 mm. The number of seg- 

 ments does not exceed 120. There is no indication of any change in the 

 structure of parapodia, in the setae and the eyes. Nor does the posterior 



