320 In trod net ion to A n imal Morphology. 



intestinal, and infundibular branches, and in the head 

 ophthalmic and tentacular vessels, which may be 

 united by an annular vessel round the mouth. The 

 visceral aorta supplies the liver and genital organs, 

 and in Ommastrephes gives off a pair of branches to 

 the fins (pinnal), which are dilated into accessory cir- 

 culatory organs. The arteries end in capillaries and 

 laminae which open into the veins, \vhich vary in 

 almost every genus. The brachial veins form a cir- 

 cular sinus at the base of the arms, and send a cephalic 

 vein upwards, which receives pallial and visceral 

 veins, and branches from the large lacunae ; it then 

 divides into two (Dibranchiata) or four (Tetrabran- 

 chiata) branches, which go to the two or four gills. 

 In Dibranchs these are dilated at the bases of the 

 trills, and surrounded by muscular fibres, forming a 

 pair of branchial hearts. The gills are pyramidal, 

 non-ciliated, in the mantle cavity, and consist of 

 united lamellae or of complexly folded dermis, bathed 

 by sea-water, which passes in and out of the mantle 

 chamber in swimming. 



The branchial veins from these dilate, and form the two or 

 four auricles of the heart. The blood is colourless, and con- 

 tains rupjHT. On the branches of the cephalic vein, before 

 they form the branchial hearts, there are spongy renal ap- 

 pendages containing caeca and often yellow or violet concre- 

 tions projecting into the aquiferous lateral sacs of the mantle 

 cavity, and communicating with the pericardium. These 

 may be the homologues of the organs of Bojanus or of the 

 gasteropod kidney, the spongy venous processes resembling 

 the spongy glandular part of that organ, or they may be 

 kidneys of another type. Over the surface are certain aqui- 

 ferous pores, by which water enters the lacunas and mi\ 

 with the blood ; these may be cephalic (or a pair on the back 

 of the head), as in Philonexis, Tremoctopus, Argonauta, or 



