484 THE INVERTEBRATA 



described here as follows : the ventricle pumps arterial blood through 

 a single aorta which soon divides into an anterior aorta supplying 

 the buccal cavity and a posterior which supplies the visceral hump. 

 The terminal branches of these arteries eventually communicate with 

 the haemocoele (dotted in Fig. 357) and in its turn this discharges 

 into the cir cuius venosus leading to the lung and heart. 



Fig. 358. Helix pomatia. A, Section of alveolus of the digestive gland. 

 ab.c. absorptive cells; calx, calcareous cells; cil.c. ciliated cells of liver tube; 

 f.c. ferment cells. After Meisenheimer. B, Diagrammatic side view of animal 

 dissected to show the alimentary canal and nervous system. Original. An. 

 anus; ao. aorta; au. auricle; buc. buccal mass; buc.g. buccal ganglion; ce.g. 

 cerebral ganglion; cr. crop; dig.gl. digestive gland; d.d. openings of digestive 

 ducts (the ducts represented by black lines); F. foot; h.gl. hermaphrodite 

 gland; int. intestine; k. kidney; muc.gl. mucous gland; n.n. nerve net in 

 surface of foot; oc.ten. oculiferous tentacle; ot. otocyst; pa.g., ped.g., pl.g. 

 parietal, pedal and pleural ganglia; pal.n. pallial nerve; rad.s. radula sac; 

 sal.d. salivary duct ; sal.gl. salivary gland ; spt. spermatheca (duct broken off 

 short); st. stomach; va. valves directing food into digestive ducts; ven. 

 ventricle; vis.g., vis.n. visceral ganglia and nerve. 



The alimentary canal (Fig. 358) commences with the buccal mass. 

 On the roof of the mouth is a small transverse bar, the jaw, and in 

 conjunction with this works the radula, which is a strip of horny base- 

 ment membrane on which are fastened many rows of minute recurved 

 teeth. It is formed in a ventral diverticulum of the buccal cavity called 

 the radula sac (Fig. 359) in which proliferating tissue is constantly 



