330 THE CRUSTACEA. $ 279. 
and the palpiform maxillae, with only a few exceptions are wholly want-- 
ing. 
§ 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 different 
layers, of which the outer, answering to a peritoneal envelope, consists ofa 
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 gtanulo-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 cesopliagns, 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. 
poda and Phyllopoda, it is straight 
9 Nordmann, loc. cit. Taf. I-III. (Lamproglena 
and Ergasilus); Rathké, De Bapyro &c. p. 4, 
Tab, I. and Nov. Act. Nat. Cur. XX. p. 42, 103, 
Tab. II. V. (Nicothoé and Phrysus) ; also 
Kroyer, Isis, 1841, p. 343, Taf. V. fig. 7. c. (Wico- 
thoz). There is an exception in this respect with 
Dichelestium. Its proboscis is prolonged into a 
kind of beak surrounded by numerous movable 
processes, of which one pair of denticulated stylets 
concealed in a fold of the proboscis corresponds per- 
haps to mandibles, while another pair may per- 
haps be regurded as maxillae; see Rathké Nov. 
Act. Nat. Cur. XIX. p. 186, Tab. XVII. fig. 12- 
14, and Milne Edwards, Hist. d. Crust. Pl. 
XXXIX. fig. 4, a-c. or Cyclop. of Anat. loc. cit. 
p. 773, fig. 412-415. 
1 Glomeris and Lynceus form here an excep- 
tion. With the first, the intestine has one curve in 
front and another behind (Brandt, in Miller's 
* [§279.] The alimentary canal of the Cali- 
goidea, according to Dana (Report. Crust. loc. cit. 
p. 1837), is divided into four very distinct parts,—an 
cesophagus, 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. 
Bee, also, for the digestive canal of Argulus, 
with its histology, Leydig (loc. cit. Siebold and 
Kalliker’s Zeitsch. Il. p. 332, Taf. XIX. fig. 2). 
— Eb. 
+ [§ 279, note 4.] For details upon the struc- 
ture of the digestive canal of Artemia and Bran- 
chipus, see Leydig (loc. cit. Siebold and Kélli- 
With the Siphonostoma,* and many of the Lophyro- 
throughout; but with the Daph- 
Arch. 1857, p. 322, Taf. XII. fig. 2); with Lyn- 
ceus, it has one or two spiral turns (Midler, En= 
tomostr. Tab. IX. X., and Jurine, Hist. d. Mono- 
cles Pl. XV. XVI.). 
2 The Cirripedia form an exception to this rule 3 
their anus is situated between the last pair of cirri 
and the base of the tail ; see Cuvier, Mém. loc. cit. 
fig. 7, k., and Martin St. Ange, loc. cit. Pl. IL. fig. 
4, 5, ke., h. 
8 ‘See Schmidt, Zur vergleich. Physiol. p. 30. 
4 For the straight intestine of the Penellina, 
Lernaeodea, and Lrgasilina, see Nordmann, loc. 
cit. Taf. I.-X., also Burmeister, Nov. Act. Nat. 
Cur. XVII. P- 311, Tab. XXIV, A. fig. 1. (Ler- 
naeocera); Rathké, Ibid. XIX. p. 156, ‘Lab. 
XVIL fig. 2 (Dichelestium) ; Jurine Hist. d. 
Monocl. Pl. I-VII. (Cyclops and Cyclopsina) ; 
Prevost, Ibid. Pl. XX.-XXII. (Chirocephalus) ; 
Joly, loc. cit. Pl, VIL. VILL. (Artemia). t 
ker’s Zeitsch. IIT. p. 283). This observer divides it 
into three distinct portions: @sophagus, 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 intimate 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. VIII. fig. 6, 10.— Ep, 
