6 WORMS. 



the apparent number of rings. The scholars should 

 next observe that this segmented body is divided into 

 three parts. The anterior portion (Fig. i, / 1) tapers 

 to a blunt point, and has the largest rings. The thick- 

 ened middle portion (Fig. I, n) is known as the " cli- 

 tellum " or " saddle." The posterior part ( Fig. i, / 2) 

 consists of segments of nearly uniform size, excepting 

 a few at its extreme end, which are broader and flatter 

 (Fig. 1,7.-). 



A thin, tough cuticle composed of the peculiar sub- 

 stance, chitine, similar in appearance to horn, covers 

 the whole body. This may be easily removed from 

 alcoholic specimens which have lain in water two or 

 three hours. 



The brownish-red color of the exposed back of the 

 worm, and the paler hue of the belly, should be ob- 

 served, together with the beautiful iridescence of the 

 cuticle. This iridescence is due to the breaking up 

 of the rays of light by reflection from the many fine 

 ridges running parallel to each other, and which may 

 be observed by putting a piece of the cuticle under 

 the microscope. These are really minute folds of the 

 transparent, outer skin, and can be made to flatten 

 out and disappear by stretching the specimen. The 

 iridescence, at the same time, vanishes, proving that 

 the brilliant play of colors is wholly due to the mechani- 

 cal, file-like structure of the surface upon which the light 

 falls. 



The intestine can be seen as a dark streak in the 

 interior, extending the whole length of the body, and 

 opening through the last segment. Lying above the 

 intestine is the blood-vessel, known as the pseudhaemal 



