138 WORMS. 



Mechanical Movements of Blood Vessels. The me- 

 chanical action of the parts concerned in nutrition can 

 best be understood by studying them in a live worm. 

 Small specimens can be found so nearly transparent, that 

 the blood vessels can be seen from the outside, and their 

 pulsations watched with a lens. But it will be found 

 more satisfactory to study these things in a large living 

 specimen that has been stilled with chloroform or ether. 

 Pin the specimen out in the dissecting pan in a |-per-cent 

 salt solution, as before directed, and open it by a longi- 

 tudinal cut a little to one side of the median dorsal line. 



Expose the blood vessels, and observe their contrac- 

 tions. Note that the contractions pass along the vessels 

 in successive waves, which mark the course of the blood 

 in them. Their red color is due to the blood they con- 

 tain, and the color of the blood is in its liquid part 

 (plasma), and not in its corpuscles. 



These and other contractions, sometimes observable in 

 the alimentary canal, are performed by the automatic action 

 of muscles within the walls of the organs themselves. 

 These, contracting, push the contents forward, much as 

 water in a rubber tube would be pushed forward if the 

 tube were drawn tightly between the fingers. 



Development. The eggs of the earthworm are laid in 

 May or June, and may be found at that time, a number 

 together, inclosed within ovate, tough, yellowish or brown 

 capsules, in- loose earth, beneath logs and stones. These 

 capsules are formed in the following peculiar manner : 

 Certain glands of the clitellum become very active at this 

 season, and pour out on the surface of the body a fluid 

 which hardens into a tough membrane, forming a girdle 

 about the body. A thick jelly-like fluid is retained 

 within this girdle, between it and the body. The girdle 

 is gradually worked forward, toward the head. When 



