594 



THE INVERTEBRATA 



head by a very important vessel, the vena cava^ which splits in the 

 kidney region into two branchial veins, which run to the so-called 

 branchial hearts, special muscular dilatations which pump blood 

 through the capillaries of the ctenidia. The blood which is oxygenated 

 there is sucked out of the ctenidium by the expansion of the auricle. 

 Blood is also returned directly to the branchial heart from the mantle 

 by the abdominal veins (and a smaller pair), and by the unpaired 

 genital and ink sac veins which run first into the right branchial vein. 



pan.' 



coec 



Fig. 405. Vertical section of Sepia officinalis to show the relation of the divi- 

 sions of the coelom. After Grobben. coec. coecum; dig.gl. digestive gland 

 (" liver ") ;/m. funnel \g.coe. genital coelom ; h. heart ; i.s. ink sac ; k.pap. external 

 opening of kidney; k.t. excretory tissue; nid. nidamental gland; o. ova; pan. 

 "pancreatic" tissue surrounding the duct of the digestive gland; pcd. peri- 

 cardium; r.p.a. opening into the kidney of the renopericardial canal, r.p.c; 

 sh. shell; Z), dorsal; V, ventral. 



In describing the alimentary system it must first be mentioned that 

 Sepia, as a type of the Decapoda, possesses ten tentacles of which the 

 fourth pair are longer than the others. These two tentacles have a 

 slender stem and a swollen terminal portion to which the suckers are 

 confined. Each tentacle can be rapidly extended and attached to the 

 living prey, and with equal rapidity retracted into a pit near the 

 mouth, thus bringing the food into the reach of the other tentacles, 

 which hold it while it is being devoured. Round the mouth are frilled 

 lips and just within it are the characteristic beaks, corresponding to 

 the jaws of the gasteropod, which bite upon each other. The buccal 



