50 Practical Zoology. 



surface ; does it appear equally comfortable in both conditions ? 

 Try also the effect of heat and cold, dust, mud, water, etc. 



8. Observe along the middle of the back a blood tube ; watch 

 its pulsations. Can you discover any other evidences of circula- 

 tion of blood ? 



EXTERNAL FEATURES OF THE EARTHWORM. 



1. The end that usually goes foremost is the anterior end; the 

 other end is the posterior end. Are the two ends of the same 

 color? The surface on which the earthworm ordinarily rests is 

 the ventral surface ; the surface usually uppermost is the dorsal 

 surface. The earthworm has right and left sides, that correspond 

 to each other ; such an animal is bilaterally symmetrical. 



2. The earthworm is segmented, or marked off into rings called 

 segments. How many segments has your specimen? Are the 

 segments all equal in width? 



3. About one fourth or one fifth of the length from the head 

 observe a place where the segments are less distinct, often enlarged 

 and with a different color. This is the girdle, or clitellum. How 

 many segments does it occupy ? How many segments are anterior 

 to it? 



4. Is the worm exactly cylindrical, that is, is the cross section 

 a circle? 



5. At the anterior end find the mouth. Overhanging it is a 

 sort of upper lip called the prostomium. At the posterior end find 

 the anus. Is it circular ? 



6. Find the rows of bristles on the sides and ventral surface. 

 How many rows are there and how many bristles in a segment ? 



7. On the ventral surface of about the fourteenth segment are 

 the rather distinct openings of the oviducts, and on the fifteenth 

 the openings of the sperm ducts. Between the ninth and tenth 

 segments are the openings of a pair of sperm receptacles, and 

 another pair open between the tenth and eleventh segments. 

 The positions of these openings vary in different kinds of earth- 

 worms, and they are 'not always easily discovered. 



