55 



enclosed in their common envelope, lie wholly outside and 

 ventral to the sinus (fig. 53, S 2 V 2 ). The anterior aorta 

 penetrates into the latter at the anterior end of the 

 stomach, and runs therein, leaving it only after its 

 anterior bifurcation. Several small infoldings of skin 

 attach the stomach to the wall of the sinus, forming small 

 mesenteries (fig. 53, Mes.). The two abdominal veins 

 running from this cavity to the venae cavae, leave it 

 dorsally, one at each side, towards the anterior end of 

 the stomach (fig. 53, Abd.Y .). Thus the blood from the 

 sinus is drained off by these, and passes direct to the 

 lateral venae cavae, and thence to the gills. 



'>>. The posterior division contains the spiral caecum, 

 which is attached to its wall by several small mesenteries. 

 The anterior wall of this region is common to it and the 

 middle division, but forms only an incomplete septum, 

 allowing free passage of blood, as it is pierced dorsally and 

 ventrally by a row of rather large holes (fig. bo, Lac). 

 The intestine soon after its origin pierces the wall of the 

 middle region, and then bending up over the ventral 

 surface of the liver, lies wholly outside the sinus (fig. 53). 

 The two hepatic ducts pierce the wall of the posterior 

 region, and uniting inside this part of the sinus, enter the 

 spiral caecum. Into the adjacent portions of the venous 

 sinus open small veins from the buccal region, lips, 

 surface of the brain, and the different organs of the 

 alimentary canal which float freely in the sinus. 



RESPIRATORY SYSTEM. 



(I) Respiration. 



The respiration of Eledone appears to agitate the 



whole of the trunk. Water enters the mantle cavity by the 



anterior opening during the period of inspiration, when 



the sides of the body may be seen to swell outwards. At 



