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 

 adiposion, so common in insects. 



The fat 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 ^ody 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 . vesiculiform, 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 eifused into the 



9 For tlie liver of the common crawfish, which is 

 large but contained in the cephalothorax, see tlie 

 descriptions and figures of Roese/, Suckmv, 

 Gevcke, Brandt ^ and Sc/ilemm, also those of Mul- 

 ler (De Clland. Struct, p. 69). This last mentioned 

 author found the liver conformable with that of 

 many of the other Macrura and Brachyura. Milne 

 Edwards (Hist. d. Crust. PI. IV. fig. 5) has found, 

 with Mala, a liepatic mass very remarkal)le in being 

 symmetrically divided into several lobes. With 

 Pagurus, there is, on each side of the pylorus, a 

 long biliary vessel, which extends along the intes- 

 tine to the extremity of the tjiil, and into which 

 numerous lateral follicles empty their product ; see 

 Swammcrdamm., loc. cit. p. 86, Taf. XI. fig. 4, 5 ; 

 Miiller, De Gland. &c. p. 70, Tab. VIII. fig. 12, 



13 ; and Delle Chiaje, Descriz. &c. Tav. LXXXVI. 

 fig. 6.* 



1 These fat-globules, of an orange color, are often 

 found scattered about in Cyclops, Daphnia and 

 Gammarus. 



'■i Such lobes and of a blue color are found with 

 Branchipus on the sides of the digestive canal. 

 Other whitish adipose masses form a kind of net- 

 work around the intestinal canal o( Lernaea, Ler- 

 naeocera and Lamproglena (Rathk^, Nov. Act. 

 Nat. Cur. XX. p. 129, and Nordmann, loc. cit. p. 

 6, 125, 132, Taf. I. fig. 4, Taf. VI. fig. 4). This 

 last observer has regarded this reticulated mass as 

 a liver. With the Jlyriapoda, these adipose 

 masses are large, lobulated, and occupy quite a 

 space in the visceral cavity. 



* [ § 281, note 9.] For the intimate structure microscope, see Leidy, Amer. Jour. aied. Sc. 1848, 

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



