INVEKTEBBATE ANIMALS. 25 



Class GASTEROPODA. 



yao-TYjp, the stomach ; ttouj, the foot. 

 Head distinct, furnished with eyes and tentacles. Body 

 usually protected by a conical or spiral shell. Lower 

 part of the body formed into a thickened, expanded, 

 creeping disc or foot. This class includes all the land 

 and most of the fresh-water and marine univalve 

 Molluscs. The latter when very young have ciliated 

 wings on the sides of the head, by which they swim 

 freely about ; the body being contained in a minute 

 spiral shell, having an operculum. — H. & A. Adams. 



Sub-class BRANCH lO-GASTEROPODA, 



^pay^iu, gills. Organs of respiration constructed to 

 breathe air suspended in water. 



Group 74.— Order HETEROPODA. 'hspog, diverse ; wuj, 

 the foot. 



This and the succeeding order are retained at the commencement of the 

 Gastekopoda because, although they may be regarded as more 

 highly organized than the Peosobeanchiata, they are less character- 

 istic members of the Branchiate Gasteropoda. 



Estimated number of species : recent, 70 ; British, 3. 

 II Examples of Oceanic Shells — Janthina, Atlanta, 

 &c., including Carinaria vitrea. 

 Upper Compartment. 

 Coloured drawings of Firola, &c. Preparations in 

 liquid of Heteropodous animals ; Janthina 

 with its raft, from which the eggs of the 

 animal are suspended. 



