334 THE CRUSTACEA. §§ 281, 282. 



reaches even to the tail, pour their secretion, by a short duct, into the 

 digestive canal on both sides close behind the pylorus. <^' 



§ 281. 



With many Crustacea, the digestive canal is surrounded with fat-cells, 

 the contents of which are often of a beautiful orange or blue color. These 

 cells either consist of a few scattered globules,"' or are disposed in lobes 

 of various forms.® This tissue is undoubtedly analogous to the Corpus 

 adrposum, so common in insects. 



The fvt which these cells contain, plays a part, probably, in digestion and 

 assimilation ; for with these animals the excess of nutriment is deposited as 

 fat to be used in times of need, as, for example, during the act of moulting. 

 This explains why the quantity found is so variable, or even may be 

 entirely wanting. 



CHAPTER VI, 



CIRCULATORY SYSTEM, 



■ § 282. 



Although the blood of Crustacea traverses the body by a very regular 

 circulation, yet, as with all the Arthropoda, the vascular system is here quite 

 imperfect, the blood-currents not always being contained in proper canals. 

 But a central, propelling organ is very rarely absent, and consists of a heart, 

 sometimes round and vesieuliform, sometimes long and tubular. With 

 the higher Crustacea, it is the point of departure of an arterial system 

 which, with the lower orders, gradually becomes abortive, and at last en- 

 tirely disappears. The more or less long arteries do not terminate periph- 

 erically in a capillary net-work, but the blood is freely effused into the 



9 For the liver of the common crawfish, which is 13 ; and Delle Chiaje, Descriz. &c. Tav. LXXXVI. 



large but contiiined in the cephalotliorax, see the fig. 6.* 



descriptions and figures of Roesel, Suckoiv, 1 These fat-globules, of an orange color, are often 



Geveke, Brandt, andSchlemm, a\sothose of Mul- found scattered about in Cyclops, Daphnia and 



ler (De Gland. Struct, p. 69). Tliis last mentioned Gammariis. 



author found the liver conformable with that of 'I Such lobes and of a blue color are found with 



many of the other Macrura and Brachyura. Milne Branchipus on the sides of the digestive canal. 



Edwards (Hist. d. Crust. PI. IV. fig. 5) has found, Other whitish adipose masses form a kind of nct- 



with Ma'ia, a hepatic mass very remarliable iu being woric around the intestinal canal of Lernaea, Ler- 



symmetrically divided into several lobes. With naeocera and Lamproglena {Ratlike, Nov. Act. 



Pafrurus, there is, on each side of the pylorus, a Nat. Cur. XX. p. 129, and Nordmann, loc. cit. p. 



long biliary vessel, which extends along the intes- 6, 125, 132, Taf. I. fig. 4, Taf. VI. fig. 4). This 



tine to the extremity of tin; t;iil, and into which last obsorver has regarded this reticuhxted mass as 



numerous lateral follicles emjity their product ; see a liver. With the Myriapoda, these adipose 



Swammcrdamm, loc. cit. p. bO, Taf. XI. fig. 4, 5; masses are large, lobulated, and occupy quite a 



Mailer, De Gland. &c. p. 70, Tab. VIII. fig. 12, space in the visceral cavity. 



• [ 5' 2S1, note 9.] For the intimate structure microscope, see Leidy, Amcr. Jour. Med. Sc. 1848, 

 of the liver of Crustacea, as elucidated by tlie XV. p. 1. — Ed. 



