Circulatmg System, 



33 



trunks. The veins of the feet and superior parts form ulti- 

 mately two of these (c), which almost immediately coalesce 



into one greater (d) ; and this vessel, after descending through 

 part of the viscera into the abdomen, and receiving blood 

 from various little tributaries, again divides into two branches 

 (e e). Each branch is here joined by a vein (o) of a size equal 

 to itself, and which has brought the blood from the abdominal 

 viscera; and a little afterwards by another, from the cloak 

 and the supports of the gills. When thus augmented, they 

 proceed to their termination in the lateral hearts, placed, one 

 on each side, at the root of the branchiae. These hearts {/) 

 are called pulmonic; they are rather cellular than fleshy in 

 texture, moderately thick, of a blackish grey colour in some 

 genera, pale red in others, and pitted internally with many 

 little cavities communicating together. Two large valves 

 are placed at the venous orifice, to prevent regurgitation ; but 

 there is none at the orifice by which the blood enters the 

 Vol. V. -- No. 23. d * 



