220 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



pedal commissure whereas the aorta is dorsal to it, so that 

 they appear to hook over the commissure. Both pass back- 

 wards obliquely towards the foot. Arriving at the surface of 

 the foot at about the level of the crop they plunge immediately 

 into it and branch into anterior and posterior trunks. The 

 former has the shorter course ; the latter can be traced almost 

 the whole length of the foot just under its inner surface. 

 It is not possible to trace the branches by dissection, but in 

 sections of small specimens they are seen to merge gradually 

 into the large and ill-defined lacunae of the foot. A large 

 branch to the parapodium (para, a) is given off from the 

 posterior branch of the pedal artery. 



5. Cephalic Arteries (ceph. a.). Cervical of Mazzarelli. 

 The paired cephalic arteries arise, like the pedal, asymmetrically 

 from the aorta. Their distribution is different on right and left 

 sides. As in the case of the pedal arteries the right cephalic 

 artery is posterior to the left in origin. The right artery 

 passes forwards or outwards, according to the degree of con- 

 traction of the animal. It sends a small branch to the blood 

 sinus surrounding the ganglia (ne. a.). Arrived at the penis 

 it branches into three. The first branch supplies the penis 

 (pn. a.) ; the second runs ventral to the penis and beyond it, 

 to the body wall (b. w. a.), the rhinophore (rh. a.) and the eye 

 (opt. a.) ; the third branch sends blood to the spermatic groove 

 (sem. gr. a.). The left cephalic artery also runs ventral to the 

 pedal ganglion, sending to it a small artery. It then goes 

 direct to the body wall, rhinophore and eye of its side. 



6. Radular Artery (rod. a.). This small unpaired artery 

 arises from the dorsal side of the aorta and runs directly into 

 the radular sac which lies immediately above it. 



7. Peribuccal or Anterior Tentacular Arteries (peribuc. a.). 

 Paired symmetrical arteries encircle the buccal mass in the 

 region where the muscle is thickest. From each artery arises 

 a branch to the labial tentacle (ant. tent. a.). 



