MOLLUSCA. 127 



the bag, it likewise penetrates the gland, and passes into 

 the veins. The arteries with which these glands are fur- 

 nished are comparatively minute. 



It appears probable that these glands separate some prin- 

 ciple from the blood, and that this is conveyed away by the 

 ejection of the water from these venous bags into the com- 

 mon 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 improbable, 

 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 con- 

 sists of fibres, which are attached to the surface 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. 



