COMMON GARDEN SNAIL (HELIX ASPERSA). 



BRITISH SLUGS— I 



By MAUD U. CLARKE 

 With Photographs by the Author 



THE Slug family are a branch of 

 the terrestrial Molliisca, in itself 

 a division of invertebrate animals 

 possessing soft bodies and an elaborated 

 organisation that places them in a higher 

 position than the insects, and only lower 

 to that of the fish tribe. 



In due form we have to recognise the 

 Slugs as of the class Cephala. sub-class 

 Gastropoda, of the order Inoperciilata and 

 sub-order Pulmonata. All four names 

 are valuable as condensed explanations. 

 The term Cephala implies a distinction 

 between molluscs possessing definite heads 

 that crawl on land, and the A cephala. or 

 aquatic molluscs, that float on water and 

 breathe through gills like fish. Gastro- 

 poda implies that the animal is a univalve 

 mcjUusc, the shell being of one undivided 

 form and having the lower surface of the 

 body constructed as a foot-sole. 



Inopercnlata impUes having no horny 

 or shelly plate, called the opercidum. with 

 which many mc^lluscs close the orifice of 

 the shell f«jr protecti(jn against enemies 

 or for warmth during cold seasons. 



The Snail has no true operculum, 



135 I Ob: 



although it coats over the orifice with a 

 secretion that hardens hke a plate during 

 the winter hibernation. 



Pulmonata has reference to the animal 

 being possessed of lungs. 



The Cephalic molluscs have a distinct 

 head and generally tentacles, or " horns," 

 with so-called " eyes " at the tips or 

 base. The " foot," or muscular disc, is 

 capable of either crawhng on the earth 

 or floating on the water, the aquatic 

 tribe forming a large separate order. 

 When deahng with the question of the 

 shell, we recognise a main division into 

 two groups, those of the Univalve and 

 Bivalve. The spiral shell of the Snail is 

 famiUar to every one as a representative 

 of the Univalve, although perhaps the 

 fact that the Slug family in several in- 

 stances are also possessed of univalve 

 shells may not be so generally known. 



Throughout the great chain of differen- 

 tiated species in the Nature world, we 

 always find links, or connecting points, 

 that show us the meaning of differences 

 between s])ecially developed families. 

 Here and there, indeed, these links are 



