NEREIS VIRENS Sars 



Material. N. virens is a common polychaete and may 

 be found in abundance under rocks between tides along the 

 Atlantic Coast. It should be anesthetized in a weak solution 

 of alcohol and preserved either in formalin or alcohol. Small 

 specimens for cross-section are best preserved either in sublimate 

 or in Bouin's picro-aceto-formalin. It is advisable to harden a 

 very large specimen in Miiller's liquid for a long time and to cut 

 it into separate segments with a sharp razor taking care not to 

 injure the parapodia. These sections can be preserved in- 

 definitely in alcohol and should be used for the study of the 

 topography of the organs under low power. 



Descriptive Part 



Nereis virens is an annulated or segmented marine worm 

 of the Class Polychaeta. The number of segments of which its 

 body is composed varies with the size and age of the worm 

 and may be less than a hundred in small specimens and up 

 to about two hundred in old and large ones. This variation 

 is due mainly to the production of new segments in the pos- 

 terior end of the worm with increasing age. The head repre- 

 sents the first segment of the worm and is sufficiently well dis- 

 tinguishable from the rest of the body. When the proboscis 

 which will be described further on, is completely withdrawn, the 

 mouth appears as a large round opening overhung by appendages 

 of the so-called prostomium. The latter forms a part of the head, 

 situated in front and above the mouth and carries two pairs of 

 eyes, two small tentacles at the end of the median lobe and two 

 large lateral palpi. That part of the head on which the mouth 



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