154 



THE ANNELIDES. 



^«^143, 144. 



CHAPTEK 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 efl'ect 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 difiiculty from 

 the dermis, but with many Capitibrauchiati, 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. ''' 



I Tlie external respiratory organs alone are 

 covered with ciliated epithelium. Orsted (Beschreib. 

 J. Plattwurmer, loc. cit. p. 77) however, affirms 

 that the body of the Nemertini is provided with 

 \ibratile cilia. But this is to me improbable at 

 least with the large species of Borlasia, N emeries, 

 and Folia. 



At all events this statement of his requires new 

 proof. See additional note under § 142. 



- Scaly appendages of this kind cover tlie back 

 uf Aphrodite, Polynoe, and Sis;alion. With 

 Polynoe squamata, they are very easily de- 

 tached. 



3 The back of Aphrodite hystrix has numerous 

 bristles and hairs ; with Aphrodite aculcnta, these 

 hairs are so thickly set that they conceal the back 

 by a kind of felt. 



1 The middle muscular sheet is found with the 

 Hirudinei and Lumliricini -, see Brandt and Rat- 

 zeburs:, Med. Zool. II. p. 244, Taf. XXIX. fig. 1, 

 2, and Morren, loc. cit. p. 83. 



But with the Nemertini it is wanting ; see 

 Rathki, Neueste Schrift. d. natvu-f. Gesellschaft, in 

 Danzig, loc. cit. p. 95. 



