1 903-1 904] Exhibits in Natural History. 147 



The head is also well developed. It bears two pairs of 

 retractile tentacles — a smaller lowermost laMal pair situated 

 at the sides of the mouth, and a longer dorsally placed ocular 

 pair, at the summit of each of which there is borne a minute 

 black eye. 



When the shell is removed there is found the mantle, which 

 is another feature of importance. It forms the roof of the 

 pulmonary chamber or lung-sac. In the water-snail "the lung- 

 sac functions also as a hydrostatic organ. 



The aperture of the mouth is bounded by soft fleshy lips. 

 It leads into a spacious buccal cavity, the walls of which are 

 excessively thick and muscular. A denticulate horny upper 

 jaw or beak is present, and the floor of the mouth is raised up 

 into a cushion - shaped odontophore, which is in turn sur- 

 mounted by a dentigerous lingual - ribbon or radula. This 

 ribbon has its posterior end in a sac called the radular sac, in 

 which it is renewed as its anterior end is worn away. 



The heart of the snail consists of a single auricle and 

 ventricle, the valves between them being so disposed as 

 only to admit of a current passing from the lung - sac to 

 the body. 



The snail is hermaphrodite, and the sex-organs are highly 

 complicated. It is not self-impregnating. 



As a type of the Vertebrates the Frog {Rana temporaria) 

 was taken, but want of space prevents any description. 



EXHIBITS IN NATURAL HISTORY. 



During the past session the following objects were exhibited 

 at the evening meetings : A collection of Australian shells, by 

 Mr M. H. Speedy ; specimens of radio-active substances, by Mr 

 W. C. Crawford ; specimen of radium bromide, by Dr Davies ; 

 petrological micro-slides, shown under the microscope, by Mr 

 A. G, Stenhouse ; goatsucker, by Mr Chas. Campbell ; devices 

 used in securing, rearing, mounting, and preserving moths and 

 butterflies, by Mr Gloag and Mr Ganaway ; preparations illus- 



