88 CIRCULATION, AQUirEROTJS SYSTEM. 



and Amphidesma thebranchia is single on each side, j^et divided 

 by an oblique crease into two parts, like the opposite pages of 

 an opened book. ' 



CIRCULATION, AQUIFEROUS SYSTEM. 



Cephalopoda (vii, 80, 83; viii, 87, 881 The heart (vii, 88), 

 which is placed on the haemal side of the intestine, receives the 

 blood through contractile vessels connecting it with, and equal 

 in number to the branchiae ; these may be regarded as auricles. 

 The branchiai are not ciliated, and are generally if not always 

 themselves contractile. The arteries end in an extensively 

 developed capillary system, but the venous channels retain to 

 some extent the character of sinuses. In returning to the heart, 

 the venous blood is gathered into the vena cava, a large longi- 

 tudinal sinus, which is situated on the posterior side of the body 

 close to the anterior wall of the branchial chamber, and divides 

 into a number of branchial vessels corresponding with the number 

 of branchiae. Each of these vessels traverses a chamber in com- 

 munication with the mantle-cavity (and which may be considered 

 a renal organ) ^ and that portion which comes in contact with the 

 water in the chamber becomes sack-like and glandular. The 

 pericardium and the sacks containing the testes and ovaries, 

 appear to communicate with the pallial cavity either through 

 these chambers or directly. 



The blood is a white liquid with a slight tendency' to bluish, 

 and contains water 89 per centum. Albumen 3 per centum. Salts 

 and substances incoagulable b}^ heat 1'5 per centum, Fibrine,etc., 

 •5 per centum. The blood of Octopus is blue, saline, but less 

 bitter than sea-water, and amounts to about one-twentieth of the 

 weight of the animal; it contains colorless globules, which agglu- 

 tinate together when taken out of the bod}^. The blood passes 

 from the arteries to the veins b^^ true capillary vessels, not by 

 lacunae. The heart beats about thirty-five times a minute. — L. 

 Fredericq, Archives Zool. Exp.^ vii, 535. 



Gastropoda (viii, 90, 91). The circulation varies greatly as to 

 complexity, according to the higher or lower organization of the 

 animals. In the prosobranchiates (ibid.) the circulation is the 

 most complicated, and yet compared with vertebrates, simple. 

 Arteries proceed from the heart to the various organs, where 

 they subdivide and terminate in fine capillary vessels. There 

 are no venous capillaries, and the blood flows. freely around the 

 organs in the bod}^ There are valves in the aorta and auricles 

 of the heart which permit the flow of blood onlj^ from the auricle 

 to the aorta. From the body-cavity the blood flows into veins, 

 some of which conduct to the branchiae whilst others pass directlj'- 

 to the ventricle of the heart. In some genera the arteries do not 

 all end in capillary vessels, but in a portion of them, and espe- 



