122 HANCOCK AND EMBLETOIf ON 



a second heart having a portal character. The systemic heart 

 lies immediately beneath the dorsal skin, in front of the respiratory 

 crown, and made up of an auricle and ventricle, enclosed within 

 a pericardium. An aorta branches oiF to supply all the viscera 

 and the foot ; on the stomach, genitalia, and other organs, a fine 

 arterial network has been demonstrated. From all the viscera, 

 except the liver mass, comprising liver, ovarium, and renal organ, 

 the blood finds its way into the intervisceral spaces, and general 

 abdominal cavity, from which it passes into orifices on the sides of 

 the abdominal walls, and enters an extended network of canals or 

 lacunae, forming a spongy tissue in the substance of the skin 

 This tissue is on each side drained by a venous trunk canal, which 

 passes backward, increasing in calibre as it goes, and penetrating 

 the inner surface of the skin behind the ventricle of the heart, 

 debouches into the posterior lateralangle of the auricle, as a distinct 

 isolated vein. This is the systemic circle, and it is evident that 

 the blood running in it is returned to the heart without having 

 passed through a special respiratory organ. 



It is that blood only which is returned from the liver mass that 

 circulates through the branchiae. On the liver mass vascular 

 injection shows a very close reticulation of minute arterioles, and 

 we are inclined to believe that in this organ there is a true 

 capillary system, the blood is undoubtedly conveyed away from the 

 liver by veins, ending in a common hepatic trunk, which passes 

 directly backwards to the branchiae. But this is not the whole 

 of the hepatic circulation, for venous blood also is thrown into 

 the liver mass, and that by means of the second or portal heart. 

 This heart lies beneath the pericardium, and is the vesicle of 

 Cuvier, which he thought opened at the orifice, by the side of the 

 anus. This heart is a ventricle, and receives venous blood from 

 the pericardium, as from an auricle. Yenous blood reaches the 

 pericardium through numerous minute orifices on its floor, these 

 communicate with the general abdominal cavity; below, the 

 heart is continued into a tube, the numerous branches of which 

 form with each other, and with branches of the hepatic artery, 

 a complicated net- work upon the walls of a branched cavity, 

 situated on the dorsal aspect of the liver mass, (liver and ovarium). 



