2l6 



ZOOLOGY 



its chief vessels, the branchial hearts, and in its posterior half 

 the genital gland. It is partially divided into two by an in- 



FiQ. 127. — Central 

 organs of the cir- 

 culation,*'gills, and 

 renal organs of Sepia 

 officinalis. After 

 John Hunter. 



v' V, Visceral veins. 

 a. Aorta. 

 V. Vena cava. 

 c. Ventricle. 



d. Auricles. 



e. Branchial hearts. 

 h. Branchiae. 



r. Renal organs. 



complete septum. It opens into the nephridia by a minute 

 pore on each side. 



The heart consists of a ventricle with two auricles opening 

 into it. The ventricle is continued in front into an anterior 

 aorta, which gives off vessels to the mantle and liver and runs 

 forward to the head and arms, and behind into the posterior 

 aorta, which supplies the generative organs and the fins, etc. 

 The blood passes largely by capillaries but partly by lacunar 

 spaces, into the veins. Of these, the largest is the anterior 

 vena cava, which has a ventral position and splits into two 

 branchial veins. These latter are beset with diverticula of the 

 nephridia, and they receive numerous veins which bring back 

 the blood from the generative organs, the ink sac, etc. Just 

 before they enter the branchial hearts they are joined by veins 

 from the mantle and posterior end of the visceral hump. The 

 branchial hearts are pulsating muscular enlargements at the 

 base of the ctenidia, whose contractions force the blood through 

 the gill. A mass of excretory tissue — the pericardial gland — 



