NEREIS JAPONICA. 3OI 



nature, so that the water in the vessel may now be easily changed by 

 means of a siphon. 



Text-figure 2. 



AB C 



Early stagers of segmentation. 



A. — Completed two-celled stage seen from the lower pole. 140/1. 



B. — View from the upper pole after completed second cleavage. 140/1. 



C. — View from the upper pole after completed third cleavage. 140/1. 



/Polar bodies are not indicated. All the figures \ 

 ^are drown from the living egg. / 



About 90 hours after fertilization the setae begin to appear. 



One of the embryos of about 9 days age is represented in the text- 

 figure (3) ; it is provided with four pairs of setigerous parapodia, a pair of 

 tentacles, a pair of tentacular cirri and a pair of short anal cirri. The two 

 pairs of the " anlagen " of the eyes are distinctly seen on the postero- 

 lateral parts of the head ; a pair of jaws, each with three teeth, may also 

 be seen already in this stage of development. 



The embryos, at about this stage of development, begin to sink down 

 gradually through the water, in which they have been reared ; and about 

 two days later, most of the embryos have sunk down to the bottom to 

 enter into the sedentary life. 



3. Observation on the Sivarntiny. 



With respect to the swarming habit of the mature worm, it has long 

 been known from the experience of fishermen in the locality that the 

 swarming occurs during the month of December, usually in one period 



