154 THE ANNELIDES. <§.*§> 143, 144. 



CHAPTER I. 



CUTANEOUS SYSTEM. 



§143. 



The skin of the Annelides consists of a very thin, non-ciliated epidermis,'" 

 and a more or less compact dermis composed of solid, but delicate fibres 

 obliquely intertwisted. 



The iridescence and often splendid colors of many of the Chaetopodes, 

 are not due to a pigment, but to an optical eifect produced by the reticu- 

 lated union of the dermic fibres. 



But the Apodes, on the other hand, owe their many colors to a pigment 

 net-work and cells. Usually the epidermis is separated with difficulty from 

 the dermis, but with many Capitibranchiati, and Dorsibranchiati, the oppo- 

 site is true. With the Apodes, the skin is closely united with the subja- 

 cent muscular layer. 



With many Dorsibranchiati, the skin has filiform or lamellar appendages 

 sometimes so much developed that they overlap each other like scales.'^ 

 With some Chaetopodes, there are, beside the bundles of locomotive bris- 

 tles and hairs, numerous appendages of this kind covering most of the 

 body.<3) 



CHAPTER II 



MUSCULAR SYSTEM AND LOCOMOTIVE ORGANS. 



§ 144. 



The muscles of the Annelides, although highly developed, are never stri- 

 ated. 



The whole body is enveloped by a subcutaneous muscular layer divisi- 

 ble into three sheets : an external, of circular fibres ; an internal, of longi- 

 tudinal fibres; these are the most developed. Then a middle one com- 

 posed of obliquely intertwisted fibres ; this is less distinct, and sometimes 

 entirely wanting.'" 



1 The external respiratory organs alone are S Ihe buck of Apkrodite hystrix has numerous 



covered with ciliated epitlielium. Orsted (Beschreib. bristles and hairs ; with Aphrodite acu/eala, these 



d. Plattwiirmer, loc. cit. p. 77) however, aflinns hairs are so thickly set that they conceal the back 



that the body of the Nemertini is provided with by a kind of felt. 



vibrutile cilia. But this is to me improbable at 1 The middle muscular sheet is found with the 



least with the large species of Bor/ostOjiVemertes, Hirudinei and Lumbricini ; see Brandt anil Rat - 



and Polia. zcbur^, Med. Zool. II. p. 244, Taf. XXIX. fig. 1, 



At all events this statement of his requires new 2, and Morren, loc. cit. p. 83. 

 proof. See additional note under ^ 142. But with the Nemertini it is wanting ; see 



- Scaly appendages of this kind cover the back Rathki, Neueste Schrift. d. naturf. Gesellschaft, in 



of Aphrodite, Potynoi:, and Sisalion. With Danzig, loc. cit. p. 95. 

 Polynoe squamala, they are very easily de- 

 tached. 



