I)itroduction to Ammal Morphology. 273 



like process, in front, many unequal sucker-like ten- 

 tacles : its fore and hinder openings have sphincter 

 muscles. The front of the head is joined to the buccal 

 region by a narrow pseiido-collum. Eight radiating 

 ciliated tentacles surround the mouth, into which two 

 salivary glands, and two, ciliated, glandular, buccal 

 pouches open. The buccal cavity is guarded in front 

 by a valve, and contains an oval, wide radula of 25-30 

 joints, each of five plates, the median one-toothed, the 

 inner lateral uncinated, the outer lateral unarmed ; it 

 lies on a tongs-shaped lingual cartilage whose branches 

 are approximated below by one transverse adductor, 

 and divaricated by two sheathing muscles. Two ru- 

 dimental conchiolin-covered pharyngeal jaws oppose 

 the radula. The oesophagus is short, the stomach 

 gizzard-like, receiving the paired bile ducts ; the 

 glandular intestine has a primary neural flexure, and 

 forms three folds under and parallel to the oesophagus, 

 finally passing between the two organs of Bojamis^ 

 and through the anal sinus to its termination behind 

 the foot. The liver is large, triangular, of one (Sipho- 

 nodentalium) or two (Dentalium) lobes consisting of 

 caeca lined by large, polygonal, coloured cells. 



There is no heart, but the colourless blood accu- 

 mulates in five, wall-less, lacunary sinuses, anal (the 

 largest), post-abdominal, buccal, cervical, and pedal. 

 From the post-abdominal sinus, it enters an anterior 

 mantle vessel, forming a vascular ring, from which, 

 and from the other sinuses, richly netted lacunae pass 

 into the mantle and foot, which act as breathing organs, 

 there being no gills. The anal sinus has a pair of 

 outer openings, one on each side of the anus, whereby 

 water is admitted. 



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