330 



THE CRUSTACEA. 



§ 279. 



and the palpiform maxillae, with only a few exceptions, are wholly want- 



ing. 



(9) 



§ 279. 



The Intestinal Canal with nearly all the Crustacea, traverses the body 

 without convolutions on the median line,"* and the anus is situated at the 

 extremity of the tail.<-> Its walls are composed of three to four difi'erent 

 layers, of which the outer, answering to a peritoneal envelope, consists of a 

 dense fibrous membrane. 



The internal layer consists of a structureless, transparent epithelium, 

 always non-ciliated. In the anterior portion of the intestine, which is 

 often dilated into a kind of stomach, as also in the rectum, this epithelium 

 is quite dense and is directly continuous with the external skin, and like 

 it also, contains chitine ; it is moreover, cast off, at the moulting, with 

 the skin to which it remains attached, partly by the mouth, and partly by 

 the anus.*''' Between this epithelium and the peritoneal envelope, there is 

 a granulo-vesicular, mucous layer, surrounded by smooth, simple, and in- 

 terlaced, muscular fibres. 



With the higher Crustacea, alone, the digestive canal consists always of 

 a very short oesophagus, a stomach, an intestine and rectum. With the 

 lower Crustacea, it is only a simple tube of the same calibre throughout, 

 except near the anus where it is sometimes constricted by the accession of 

 a muscular layer. With the Siphonostoma,* and many of the Lophyro- 

 poda and Phyllopoda, it is straight throughout ; '^' but with the Daph- 



9 NoTdmann, loc. cit. Taf. I. -III. (Lamproglena 

 and Ergasilus) ; Rathki, De Bnpyro &c. p. 4, 

 Tab. I. and Nov. Act. Nat. Cur. XX. p. 43, 103, 

 Tab. II. V. (Nicothoe and Pkryxus) ; also 

 Krijijer, Isis, 1841, p. 343, Taf. V. fig. 7. c. {Nico- 

 thoe). There is an e.xception in tliis respect with 

 Dichele.'itium. Its proboscis is prolonged into a 

 kind of beak surrounded by numerous movable 

 processes, of wliich one pair of denticulated stylets 

 concealed in a fold of the proboscis corresponds per- 

 haps to mandibles, while anotlier pair may per- 

 haps be regarded as maxillae ; see Ratliki Nov. 

 Act. Nat. Cur. XIX. p. 136, Tab. XVII. fig. 12- 

 14, and Milne Edwards., Hist. d. Crust. PI. 

 XXXIX. fig. 4, a-c. or Cyclop, of Anat. loc. cit. 

 p. 773, fig. 412-415. 



1 Glomp.ri.'s and Lynceus form here an excep- 

 tion. With the first, the intestine has one curve in 

 front and another behind {Brandt, in Mu/ler's 



* [ § 279.] The alimentary canal of the Cali- 

 goidea, according to Dana (Report. Crust, loc. cit. 

 p. 1337), is divided into four very distinct parts,— an 

 CBSophagus, small and slender ; a stomach broad 

 and heart-shaped ; an intestine, marked by light 

 constrictions, and a rectum provided with power- 

 ful muscles. The oesophagus has a valve at its 

 entrance into the stomach, and thereby regurgita- 

 tion of the food is prevented. 



See, also, for the digestive canal of Argulu.i, 

 with its histology, Leydig 'loc. cit. Siebold and 

 Kolliker's Zeitsch. II. p. 332, Taf. XIX. fig. 2). 

 — Ed. 



t [ § 279, note 4.] For details upon the struc- 

 ture of the digestive canal of Arlcmia and Bran- 

 chipus, see Leydig (loc. cit. Siebold and Kolli- 



Arch. 1837, p. 322, Taf. XII. fig. 2) ; with Lyn- 

 ceus, it has one or two spiral turns {Muller, Eii- 

 tomostr. Tab. IX. X., and Jurine, Hist. d. Mono- 

 cles PI. XV. XVI.). 



2 The Cirripedia form an exception to this rule ; 

 their anus is situated between the last pair of cirri 

 and the base of the tiiil ; see Cuvier, Mem. loc. cit. 

 fig. 7, k., and Martin St. Ange, loc. cit. PI. II. fig. 

 4, 5, &c., h. 



S See Schmidt, Zur vergleich. Physiol, p. 30. 



■4 For the straight intestine of the Penellina, 

 Lernaeodea, and Ergasilina, see Nordmann, loc. 

 cit. Taf. I.-.X., also Burmeister, Nov. Act. Nat. 

 Cur. XVII. p. 311, Tab. XXIV. A. fig. X. (Ler- 

 naeocera) ; Rathk^, Iliid. XIX. p. 156, Tab. 

 XVII. fig. 2 {Dichelestium) ; Jurine Hist. d. 

 Monocl. PI. I.-VII. {Cyclops and Cyclopsina) ; 

 Prevost, Ibid. PI. X.X.-XXII. {Chirocephalas) ; 

 Joly, loc. cit. PI. VII. VIII. {Artemia). t 



i-er's Zeitsch. III. p. 2S3). Thisobserver divides it 

 into three distinct portions : CEsophagus, Stomach, 

 and Intestine. The stomach is composed histologi- 

 cally of four tunics ; 1. A Muscular, made up of 

 circular and longitudinal muscles ; 2. A Homoge- 

 neous, serving as a support for this organ ; 3. A 

 Cellular ; and lastly 4, A Homogeneous, which ap- 

 pears to be merely a continuation In words of the 

 external Chitine layer. The intunate structure of 

 the intestine is quite the same as that of the stom- 

 ach, but the elementary particles of the muscles 

 composing its muscular tunic, are spindle-shaped, 

 giving this tissue here a structure quite peculiar, 

 and unlike anything found elsewhere ; see loc. cit. 

 Taf. VIU. fig. 6, 10. — Ed. 



