154 THE ÄNNELIDES. §*§> 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 effect 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 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.'^' 



CHAPTEE 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 The back of Aphrodite hy/ttrix has numerous 

 covered with ciliated epithelium. Orsted (Beschreib, bristles and hairs ; with Aphrodite aculeala, tliese 

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

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



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



least with the large species of ßor/ostOjiVemeyte«, llirudinei and Lumbricini ; see Brandt and Rat- 



and Polia. 2f'ht,rg; Med. Zool. II. p. 244, Taf. XXIX. fig. 1, 



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

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



2 Scaly ai>i)eiid.Lf,"s of this kind cover the back Rath/,-^, Neueste Schrift, d. naturf. Gesellschaft, ia 

 of Aphrodite, Polynoe, and Si^a/ion. With Danzig, loc. cit. p. 95. 



Polijnoi squamaCa, they are very easily de- 

 tached. 



