^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 surflice of this envelope sends oif 

 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 venuicu- 

 lar motions of the body, there are other groups : 1st. For the auxiliary- 

 locomotive organs, and 2nd, for many other organs. 



1. The Hirudinei are distinguished, as is well known, by a sucker 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 (aciculi), 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 ranged in many rows upon the belly, and may be wholly withdrawn into 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, Nai's has also a row of bristles each side of the 

 body.'i> 



2 These separate muscles are found in Aphro- 

 dite, Polynoe, and Nereis, with which the longi- 

 tudinal ones especially, are seen separated into 

 dorsal, ventral and lateral layers. See for the 

 subcutaneous muscles of the Branchiati in gen- 

 eral, Ratkke, De Bopyro et Nereide, p. 29, Tab. 

 II., and in the Danzig. Schrift, loc. cit. p. 62, Taf. 

 rV. fig. 6 ; also Gnibe, Zur Anat. und Physiol, d. 

 Kiemenwürmer, p. 4. et seq. 



3 When these septa are largely developed, and 

 embrace closely the digestive canal, as in Lum- 

 briciis, Sabeila, 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.* 



' The stings and bristles of the Abranchiati, 

 upon whose various forms see Örsted (Conspectus 

 generum specierumque Naidum, in Kröyer's 

 Naturhistor. Tidskrift. IV. 1842, p. 128, PI. III.), 

 are easily 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 

 K6Uiker''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 Lmn 

 bricini the stings are often detached interiorly, and 

 falling into tlie 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. II. fig. 3, and in fViegmann^s Arch. 

 1843, I. p. 196. These agglutinated masses in 

 which are lodged usually various kinds of vibrioid 

 parasites, have been taken by Montisre (Observ. 

 sur les Lombries, in the M6m. du Museum I. p. 

 246, tig. 5, 6, g) for the eggs and fcetuses of the 

 Lumbricini. Morren (loc. 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 j see loc. cit. Taf. YIII. fig. 

 13- 23. 



See also Hoist, De struct. Musoul. in genere et 

 annulat. musculis in specie, Diss. Dorpate 1846. 

 — Ed. 



