Mr C. Collier on Univalves. 229 



The tube is muscular, cylindrical, varied in colour, capable of 

 elongation from, and retraction within itself, like many tentacula 

 of moUusca and insects. The elongation is produced by the 

 successive contractions of the circular fibres, and the retraction 

 by the agency of the longitvidinal fibres, which arise from the 

 inner surface, and are attached to the foot. The length and 

 thickness vary. In most species of Murex, Conus, and Bucci- 

 num, it has been compared to the proboscis of the elephant ; in 

 others, as in certain species of Valuta and Conus, and in Bulla 

 Ovum, it is shorter and less rigid. In the former description of 

 tube, the oesophagus passes along, to be affixed to its apex, em- 

 bracing a fleshy mouth (generally without mandibles) and 

 tongue, and adapted, of course, for its changes of dimension. 

 In the latter sort, the tubes open directly into each other. 



The tongue is much alike, excepting as to length, in all : 

 pointed at the extremity, or dart-shaped, and serrated in the 

 middle, it passes, as in some reptiles, through the back of the 

 mouth, and lies extended along the oesophagus. After the spe- 

 cies of Haliotis and Patella, and some Nerita, (in which it 

 greatly exceeds the length of the animal), it is longest in the 

 Cyprtere ; in the others it does not far surpass the mouth. 



The fleshy mouth belongs to Cypraa, Bulla ampulla, Tro- 

 chus, Turbo, Strombus, Helix, Nerita, Haliotis, Patella, Ser- 

 pula, and the pyriform species of Buccinum and Murex ; the 

 tube, with mouth and tongue, to Murex, Voluta, Buccinum spi- 

 ratum, B. Cassis, B. Patulum, B. Dolium, and varieties ; the 

 tube simply to Conus, Bulla Ficus, Buccinum maculatum, and a 

 fevi others. 



The brain is formed of two ganglia (generally of a red co- 

 lour, sometimes, as in Strombtcs and Cypraa, rather of a nale 

 yellow hue), which form one mass, with a small intervening 

 white substance, or, being separate, are connected by nerves. 

 Whatever the colour may be, it is as a centre, if united, with 

 the nerves for radii ; or it forms, if separated, various figures, 

 according to the number of centres and connecting filaments. 

 It is single in Cyprcea, Strombus, Trochus, Murex, Voluta ; 

 of two ganglia, one above and another below the oesophagus, in 

 Conus ; of three in Bulla Ficus ; of five in B. ampulla. 



The oesophagus is enlarged into a crop or first stomach, in all 



