420 Pi-of. M'IntosU 07i the 



I. The Cutaneous System. 

 1. The Cuticle. 



In the snout the cuticle forms a dense translucent invest- 

 ment, thickest in the median line dorsally and diminishing 

 toward each lateral margin. On the ventral surface the same 

 arrangement occurs, but the coat is appreciably thinner. In 

 front of tlie mouth the depth of the cuticle increases in the 

 median ventral region, especially behind the separation of 

 tlie central longitudinal muscles. It then diminishes in 

 thickness and becomes continuous with the superficial layer 

 of the oral region, and will be considered under tliat head. 

 Toward the posterior end of the snout a considerable layer 

 occurs on the body-wall below the decreasing lateral expan- 

 sions, which likewise have a thicker covering than in front. 

 In the anterior region of the body it forms a well-marked 

 layer, though it is proportionally thinner than on the snout. 

 On the whole, it is thinnest on the lateral regions and the 

 lamellie l)eyond the pedicles, while it attains its maximum 

 on the ventral surface under the nerve-cords and toward 

 the median line. 



When the living animal is viewed from the ventral surface 

 the small hypodermic pads existing on the fifth, sixth, seventh, 

 and eighth segments, just in front of the transverse division 

 of the feet, cause a distinct forward arch of the cuticle in 

 the median line. The elevation on the fourth segment is 

 indistinct and the eighth is less than the seventh. At the 

 latter a pale belt is observed on each side, slanting backward j 

 to meet in the median line, and from the point of junction a i 

 single central band is continued posteriorly. Such probably 

 indicates the union of the neural canals. 



In the second or posterior region of the body the cuticle 

 is thinner than in the first, the densest part being in tlie 

 ventral median line, where the nerve-cords occur. It is very 

 attenuate at the 'tip of the tail. 



The cuticle (with the hypoderm) is thrown into very 

 regular wrinkles in contraction. Pores are very difficult to 

 see in this apparently structnreless tunic, even in the most 

 favourable regions, such as the cuticle covering the tips of j 

 the tentacles and the papillae of the same organs ; but very ,' 

 fine specks stud the cuticle of the anterior region of the body. 

 In life the surface of the cuticle shows many fine palpocils. , 



It is this coat more than any other which gives firmness j 

 and elasticity to the anuelidan surface and distinguishes it I 

 from the soft ciliated skin of the Nemerteans (toughness of : 



