CRUSTACEA. 



775 



The biliary apparatus of the Crustacea is of 

 very large size in the Decapoda. The liver is 

 symmetrical (Jig. 4 17), and consists of two 

 halves generally separate one from another, 

 and the whole organ is made up of an agglo- 

 meration of crecums, which by one of their 

 extremities empty themselves into excretory 

 ducts. These by their union form larger and 

 larger trunks, and the secreted fluid or bile is 

 finally poured by a double channel into the 

 pyloric portion of the stomach. The liver is 

 found to undergo extensive modifications as it 

 is examined in individuals lower and lower in 

 the series; in the Edriophthalmians, finally, 

 we discover nothing except three pairs of bili- 

 ary vessels analogous to those of insects. 



The liver is not the only secerning organ 

 whose product is poured into the intestine. 

 On each side of the pyloric portion of the 

 stomach, we observe two blind tubular cavi- 

 ties narrow and much elongated in their form, 

 which pour out a whitish fluid (jig.^\6,J\f); 

 and at the point of conjunction of the two por- 

 tions of which the intestine frequently consists, 

 as has been said, there is a third tubular cavity 

 or vessel in all respects similar to these two 

 (fig- 416, g). These tubuli are all wanting in 

 the Astacus fluviatilis, and in the Astacus ma- 

 rinus the single posterior tubulus is the only 

 one found. Nothing positive is known with 

 regard to the uses of the fluid secreted in these 

 tubuli. 



To conclude, there are two organs of a green 

 colour situated on either side of the oesopha- 

 gus, the structure of which is glandular, and 

 which appear to bear some analogy to the sali- 

 vary glands. 



B. Of the blood and circulation. We are 



altogether without positive information as to 

 the mode in which the nutritious fluid, elabo- 

 rated by the process of digestion, passes from 

 the intestinal canal into the torrent of the cir- 

 culation. Hitherto no chyliferous vessels have 

 been detected, and we are therefore led to 

 believe that it is by imbibition that the trans- 

 ference takes place from the intestine to the 

 bloodvessels in the Crustacea. 



The blood of the Crustacea is a colourless, 

 or slightly bluish coloured fluid, holding an 

 abundance of circular-shaped globules in sus- 

 pension. It is extremely coagulable. Its che- 

 mical composition has not been investigated. 



This nutritious fluid is put into motion by a 

 heart, and circulates through a vascular system 

 of great complexness. Willis,* Swammer- 

 dam,f Cuvier,]; Desmarest, and several others 

 have given a description of this system ; but 

 there are still innumerable points upon which 

 opinions remain different. The following are 

 the conclusions to which M. Audouin and 

 I have come from a careful study as well of 

 the anatomical disposition of the circulatory 

 apparatus of the Crustacea, as of the progress 

 of the blood through its interior.|| 



The circulation of the blood in these ani- 

 mals is accomplished in a manner very similar 

 to what takes place in the Mollusca. The 

 blood pushed forward by the heart is distri- 

 buted to every part of the body, from whence 

 it is returned into large sinuses situated at no 

 great distance from the base of the branchiae ; 

 from these sinuses it is sent on to the respi- 

 ratory apparatus which it traverses, and from 

 which it then finds its way to the heart, to 

 recommence the same circle anew. The heart 

 is consequently aortic and single. 



Fig. 418. 



m 



Viscera of the Cancer Pagurus. 



f f heart ; a, ophthalmic artery ; o, abdominal artery ; c, stomach ; e, skin ; 

 g, branchiae, inverted to show the efferent vessels ; h, vault of the flancs ; 

 n, branchiae in their natural position ; m, flabellum ; I, liver j k, testicles. 



De anima brutorum, caput tertium, p. 16. 



t Collect, academique, partie etrangere, t. v. 

 p. 126. 



\ Le9ons d'Anatomie Comparee, t. iv. p. 407, et 

 Regne Animal, Ire ed. t. ii, p. 512, et t. iii. p. 5. 



$ Considerations sur les Crustaces, p. 57. 



|] Recherches anatomiques et physiologiques sur 

 la Circulation dans les Crustaces, Ann. des Sc. 

 Nat. t. 11. 



