VASCULAE SYSTEM OF MOLLUSCA. 



373 



from tlie coelom is collected into canals, wliicli run in tlio integu- 

 ment; and thence it is distributed to the gills. All the blood, how- 

 ever, does not pass to them, for some is returned to the heart after 

 having passed through the integument. 



In Helix and Limax the htemal spaces, which pass into the wall 

 of their branchial cavity, and which form a system of canals which 

 carries blood to the res- 

 piratory organs, are de- 

 veloped in a vascular 

 manner. They break 

 up into a rich network 

 in the integument, and 

 this network gives off a 

 number of large trunks 

 with distinct walls, 

 which nnite to form a 

 " pulmonary vein ; " 

 and this vein passes 

 into the auricle. The 

 network of pulmonary 

 vessels may be regarded 

 as a large blood sinus, 

 which extends into the 

 walls of the lungs, and 

 which is broken through 

 at various points by 

 islets of firm substance. 



287. 



The heart of the 

 Cephalopoda is placed 

 at the base of the vis- 

 ceral sac, and is formed 

 of a rounded or trans- 

 versely - oval ventricle 

 (Fig. 195, J? 0; Fig. 199, 

 c), which receives blood 

 from as many bi'an- 

 chial veins as there are 

 branchiae. That is to 



say, in Nautilus there are four, and in the rest of the Cephalopoda 

 two branchial veins opening into the ventricle. These veins are 

 generally considerably widened out in front of their opening into the 

 ventricle (Fig. 199, v hr), and this enlargement is homologous with 

 the auricle in the Gastropoda and Lamellibranchiata. Two arterial 

 trunks always arise from the heart ; one, the larger, passes straight 

 forwards ; this is the arteria cephalica (Fig. 199, a) ; at some dis- 

 tance from it a smaller trunk, the arteria abdominalis {a') is given 



Fig. 199. Anatomy of Octopus. Mantle-cavity and 

 visceral sac, opened from tlie ventral surface, ph Pha- 

 rynx, gls s Superior salivary glands, gis i Inferior 

 salivary glands, o Eye. i Funnel, hr Branchiae. 

 or Ovary, od Oviduct, c Heart, v br Branchial veins. 

 ft Arteria cephalica. vc Vense cavse. av Venous 

 appendages (after Milne-Edwards.) 



