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APLYSIA. 213 



ascends the anal papilla, may be called the rectnm, though it 

 is not differentiated from the remainder of the gut. (Fig. 8, 

 red.) Near the anus it becomes more muscular, however, 

 and at the point where it discharges to the exterior, a sphincter 

 muscle, formed by interlacing muscle bands in the surrounding 

 tissue, occurs. Waste products are forcibly expelled by the 

 alternate relaxation and contraction of the anal sphincter, 

 and the ciliary action of the respiratory chamber, aided, if 

 necessary, by sudden approximation of the parapodial lobes, 

 removes the faecal matter from the neighbourhood of the 

 animal. 



Glands of the Gut. 



These comprise the salivary glands and the " liver." 



Salivary Glands. There are two elongated salivary glands 

 in Aplysia, and they discharge, as has already been described, 

 into the buccal cavity. Each gland is attached by connective 

 tissue to the side of the crop and passes forwards, rarely taking 

 part in the spiral coiling of the latter. Just behind the nerve 

 ring the glandular tissue stops, and the flat, thin- walled duct 

 passes through the ring as in all Euthyneura, runs parallel to 

 the oesophagus, and plunging into the muscles on the dorsal 

 side of the buccal mass opens into the buccal cavity. (Figs. 

 22 and 23.) 



In sections the glandular portion shows a simple aggre- 

 gation of secretory cells round a central duct. The duct is 

 ciliated. The salivary secretion consists largely of mucus, 

 and is not digestive. The nerve supply is drawn from the 

 buccal ganglia (Fig. 17, r. sal. n. and I. sal. oes. n.) 9 and the 

 blood supply from the gastro-oesophageal artery. (Fig. 13, 

 g. oes. a.) 



Liver. The liver, digestive gland or hepato-pancreas is a 

 compact, voluminous gland which makes up the greater part 

 of the visceral mass. With the gonad it forms, as it were, a 

 packing for the coils of the alimentary canal. In a specimen 



