154 THE ANNELIDES. $$ 148, 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 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. 
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.” 
1The external respiratory ,organs alone are 8 The back of Aphrodite hystrix has numerous 
covered with ciliated epithelium. Orsted (Beschreib., bristles and hairs ; with Aphrodite aculeata, these 
d. Plattwiirmer, loc. cit. p. 77) however, affirms hairs are so thickly set that they conceal the back 
thatthe body of the Nemertini is provided with’ by a kind of felt. 
vibratile cilia. But this is to me improbable at 1 The middle muscular sheet is found with the 
least with the large species of Borlasia, Nemertes, Hirudinei and Lumbricini; see Brandt and Rat- 
and Polia. zeburg, Med. Zool. Il. 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 
2 Scaly appendages of this kind cover the back Rathké, Neueste Schrift. d. naturf. Gesellschaft, in 
of Aphrodite, Polynoe, and Sigalion. With Danzig. loc. cit. p. 95. 
Polynoé squamata, they are very easily de- 
tached. 
