CEPHALOPODA. 



63 



the Dibranchiata in special cavities of the latter, the so-called cartila- 

 ginous labyrinth. They receive from the pedal ganglion their short 

 auditory nerves, which, however, arise in the brain. 



The respiratory organs have the form of two (Dibranchiata) or 

 four (Tetrabranchiata) pennate gills, which are placed at the sides of 

 the visceral sac in the mantle cavity. They are bathed by a current 

 of water which is continually renewed. 



The heart lies in the hinder part of the visceral sac, more or less 

 closely approximated to the apex of the body. It consists of 

 a median ventricle 

 and as many lateral 

 auricles as there are 

 gills (figs. 535 and 

 536). A large an- 

 terior aorta (aorta 

 cephalica) passes off 

 from the ventricle 

 and gives in its 

 course strong 

 branches to the 

 mantle, alimentary 

 canal, and funnel, 

 and breaksV up in 

 the head into ves- 

 sels to the eyes, lips 

 and arms. A pos- 

 teriorly directed vis- 

 ceral artery also 

 leaves the ventricle. 

 The capillary net- 

 work, which is 

 richly developed in all the organs, passes partly into sinuses, partlv 

 into veins, which are collected through lateral veins into a large an- 

 terior and a posterior vena cava. Each of these bifurcates into two 

 or four trunks (according to the number of gills) which carry the 

 blood to the gills. Immediately before their entrance into the 

 gills the walls of these so-called branchial arteries are (except in 

 Nautilus) especially muscular and rhythmically contractile and 

 constitute branchial hearts. The Cephalopoda also possess arrange- 

 ments by which a mixture of water with the blood can be effected. 



Paired kidney sacs are always present, one on each side of the 



FIG. 536, Circulatory and excretory organs of ScjxVr, qrftci'iialis 

 from the dorsal side (after Hunter) Br, gills ; C, ventricle ; Ao 

 and Ao", the anterior and posterior aorta ; V, lateral vein ; Vc>, 

 anterior vena cava ; Vc", posterior vena cava ; N, renal append- 

 ages of the veins ; Vbr, advehent branchial vessels (branchial 

 arteries) ; Kh, branchial heart ; Ap, appendage of the same ; At, 

 At', auricles receiving the revehent branchial vessels (branchial 

 veins). 



