§ 145. THE ANNELIDES. 155 
With the Apodes, this muscular envelope so closely embraces the viscera, 
that the cavity of the body is made very small. But with the Chaetopo- 
des, this cavity is larger. 
With many of the Branchiati; the muscular fibres form distinct fasciculi 
—so that instead of a common muscular envelope there are longitudinal 
and annular muscles distinct from each other.” 
With many Chaetopodes, the internal surface of this envelope sends off 
annular muscular septa into the cavity of the body, at the junction of the 
segments, — thus dividing this last into as many chambers as there are 
segments; sometimes these septa bind the intestinal canal so closely, as to 
regularly constrict it. 
§ 145. 
Besides the common subcutaneous muscles, which produce the vermicu- 
lar motions of the body, there are other groups: Ist, For the auxiliary 
locomotive organs, and 2nd, for many other organs. 
1. The Hirudinei are distinguished, as is well known, by a sueker situ- 
ated at their posterior extremity, which contains both circular and radiating 
muscular fibres. 
This sucker serves both to move and to attach the body. 
All the Chaetopodes have short, horny stings (aczculi), and long bristles. 
(setae), united in fasciculi of various forms, which they use as fulcra 
when they creep, or as oars when they swim. 
With the Branchiati, these organs are most fully developed, and are nearly 
always situated laterally upon a double row of fleshy knobs; and those of 
the two inferior rows may be regarded as rudimentary feet. 
The Lumbricini have short and usually S-shaped stings which are ar- 
ranged in many rows upon the belly, and may be wholly withdrawn into 
the abdominal cavity. 
Beside these last, Nats has also a row of bristles each side of the 
body.™ 
2 These separate muscles are found in Aphro- 
dite, Polynoé, and Nereis, with which the longi- 
tudinal ones especially, are seen separated into 
dorsal, ventral and lateral layers. See for the 
I of the B hiati in gen- 
eral, Rathké, De Bopyro et Nereide, p. 29, Tab. 
IL., and in the Danzig. Schrift. loc. cit. p. 62, Taf. 
IV. fig. 6; also Grube, Zur Anat. und Physiol. d. 
Kiemenwiirmer, p. 4. et seq. 
8 When these septa are largely developed, and 
embrace closely the digestive canal, as in m= 
bricus, Sabella, Serpula, and Eunice, there are 
always foramina in these diaphragms or septa, 
through which the contents of the cavity of the 
body can pass from one chamber into another.* 
1 The stings and bristles of the Abranchiati, 
upon whose various forms see Orsted (Conspectus 
generum specierumque Naidum, in Kréyer’s 
Naturhistor. Tidskrift. IV. 1842, p. 128, Pl. III.), 
are soy lost from use, but are as easily repro- 
duced. 
*[§ 144, note 3.} The development and inti- 
mate structure of the muscles of the Annelides has 
been carefully studied by Leydig (Siebold and 
Kiélliker’s Zeitsch. I. 1849, p. 103) upon Pisci- 
cola, Clepsine, Nephelis, and other Hirudinei. 
The muscular fibre is here developed as in the 
higher animals out of large nucleated cells arranged 
in rows, and the adult fibre often shows the relics 
The number of these organs may therefore vary 
very much upon the different segments of the same 
individual. It is remarkable that with the Lum 
bricini the stings are often detached interiorly, an& 
falling into the cavity of the body form there tough 
masses which are glued together by a viscous sub- 
stance lodged in the posterior chambers of the 
body ; see Hoffmeister, De vermibus quibusdam 
loc. cit. Tab. Il. fig. 3, and in Wiegmann’s Arch. 
1843, I. p. 196. These agglutinated masses in 
which are lodged usually various kinds of vibrioid 
parasites, have been taken by Montégre (Observ. 
sur les Lombries, in the Mém. du Museum I. p. 
246, fig. 5, 6, g) for the eggs and foetuses of the 
Lumbricini. Morren (oe. cit. p. 195, Tab. XXV.— 
XXIX.) has gone even further, by taking these 
stings for the chrysalids, and their enclosed vibrios. 
for the embryos of these animals, 
of these elementary parts. The fibre is not trans- 
versely striated, and is composed of a structureless. 
envelope or sheath which is filled with a fine 
granular substance ; see loc. cit. Taf. VIII. fig. 
18- 23. 
See also Holst, De struct. Muscul. in genere et 
annulat. musculis in specie, Diss. Dorpate 1846 
—Ep. 
