426 PHILOSOPHY OF ZOOLOGY. 



the common cavity. Were it practicable to analyse the 

 yellow mucus which these glands contain, some light might 

 be thrown on the subject. Indeed, it appears not impro- 

 bable, that this arrangement is analogous in its functions to 

 the urinary system in the most perfect classes. 



Each vena cava enters its corresponding lateral heart or 

 ventricle, through an intervening valve. Each lateral 

 heart is situate at the base of each gill, is pear-shaped, 

 black, and moderately thick, with numerous pits on its inner 

 surface. Its narrow end terminates without any valvular 

 structure in the pulmonary artery. In the genus Octopus, 

 the lateral hearts are naked ; but in the genera Loligo and 

 Sepia, there is suspended from each, by a slender footstalk, 

 a spongy round body, which is concave beneath. The 

 footstalk consists of fibres, which are attached to the sur- 

 face of the heart, but there is no communication by ducts 

 or vessels. The use of this organ is unknown. 



The animals of this class continually reside in the water, 

 and respire by means of gills or branchiae, These are 

 double, one on each side, corresponding with the lateral 

 pulmonic ventricles. Each gill is connected at its opposite 

 sides to the tunic, by means of fleshy ligamentous bands. 

 Between these, the double leaves of the gills are arranged 

 in an alternate series. Each leaf is supported by a foot- 

 stalk from the band, and is subdivided into smaller leaves, 

 to expose a greater surface to the water. 



The pulmonary artery passes along this band, sends 

 a branch into each footstalk, which, penetrating the sub- 

 stance of the gills, conveys the blood to its different divi- 

 sions. 



The systemic veins depart from the gills at the opposite 

 extremity. These unite at the inferior band, and from 

 each gill a vessel proceeds to the single central or systemic 

 heart or ventricle. In some of the animals of this class the 



