2l6 LAXGDOaW [Vol. XI. 



to a mctamere, making about 1 50,000 in the whole worm. In 

 the specimen from which the chart was made, there were about 

 1900 sense-organs on the first metamere and the upper surface 

 of the prostomium, 1200 on the tenth metamere, and 700 on 

 the fifty-sixth. These numbers are, of course, only approxi- 

 mate, but they give some idea of the great abundance of these 

 organs. 



The various zones and groups of sense-organs may be readily 

 seen with a hand lens in living specimens, unstained alcoholic 

 material, and in those stained with haematoxylin, if a large 

 worm is used for the examination. The sense-organs appear 

 as small, slightly elevated spots which reflect the light more 

 strongly than the surrounding surface. Those organs which 

 occur in line with the setae are most readily found. In the 

 study of living specimens it is interesting to note that, when 

 disturbed, the worm often draws the entire prostomium into 

 the opening of the buccal cavity, thus protecting the numerous 

 sense-organs on the prostomium as well as closing the opening. 

 During regular contraction of the earthworm, the cephalic and 

 caudal metameres, especially the former, are very much ele- 

 vated around the median part, thus bringing the median zone 

 into great prominence, while the border of adjacent metameres 

 are so closely pressed together that the cephalic zone is con- 

 cealed. This may account for the prominence of the median 

 zone at the two ends of the worm. Further support for this 

 interpretation may be found in the fact that in the metameres 

 of the middle region of the body, where the cephalic zone is 

 prominent, there is much less contraction, and consequently 

 the cephalic zone is not apt to be concealed. 



If a transparent worm about 15 mm. long be examined in a 

 watch-glass of water under a cover-glass with a 4 mm. objec- 

 tive and 4 ocular, the sense-organs may be demonstrated. As 

 the worm moves about in the little space thus formed, it is 

 possible to observe continuously particular spots on the sur- 

 face. The clusters of sense-hairs may then be distinctly 

 seen radiating outward from the rounded elevation of the cuti- 

 cula over the sense-organs. 



