XXIV IKTKODUCTION. 



position, while those below show by the direction they take the 

 pedal and visceral parts of the ganglionic mass. From the cerebral 

 parts nerves lead to the eye and oral tentacles and to the sides 

 of the mouth — one (large) to the side of the buccal mass and 

 another (smaller) to where the salivary ducts are given off from 

 it. From the pedal ganglia numerous nerves, some very minute, 

 lead to the sides of the foot, distributed along its edge ; one, 

 conspicuous and long, extends to the edge of the mantle on 

 the right side. Some of these nerves bifurcate before reaching 

 the foot. These visceral nerves thus break up and extend all 

 over the body of the animal along the course of the alimeutary 

 canal and the generative organs, &c. Laud-Mollusca possess 

 sensory organs, and their sense of touch and smell is acute, both 

 combined directing them in their search for food and hiding-places. 

 The seat of the olfactory organs is the apex of the tentacles, 

 more particularly the dorsal pair, but the ciliated surfaces of the 

 body round the mouth and respiratory aperture assist in the 

 sense of smell. 



Two auditory sacs (otocysts) are usually found situated on the 

 anterior side of the cerebral ganglia. They are lined with cilia 

 and contain minute calcareous paxlicles, called otoconia, of varied 

 forms in different genera and species. 



Alimentaey System. 



The alimentary canal is very long, extending back in a loop 

 within the apical whorls of the shell and returning forward to 

 the side of the respiratory orifice (fig. i, B). In different genera 

 there is considerable difference and complexity in the way in which 

 it is coiled. The fore portiou, called the foi-e gut, iucludesjthe buccal 

 cavity. The narrow oesophagus or gullet leaves this on the dorsal 

 side, passes through the nervous collar, and expands into the crop. 

 ■Spread upon this are the salivary glands (fig. 2, sg, p. 3), gene- 

 rally paired but sometimes coalesced together ; fine ducts, one on 

 either side, called the salivary ducts, connect them with the buccal 

 cavity (6). The fore gut contracts and again enlarges into the 

 mid gut or stomach {st), and here a duct connecting it with the 

 anterior {al) and posterior lobes of the liver occurs, and at about 

 midway in its length the coils of the intestine buried in the poste- 

 rior lobes (^^Z) return again and continue in a long straight 

 portion of the rectum to the anus (o), which in shell-bearing 

 forms is near the upper and inner angle of the aperture or near 

 the junction of the right and left dorsal lobes ; in the more slug- 

 like forms {Austenia and Girasia) it is on the side of the body. 

 Where the shell has become reduced, as in these two Indian 

 genera of the Zonitidae, the viscera never occupy the foot to its 

 terminal end, as is seen in Limax and other Palsearctic genera. 



The Buccal Mass. 



This lies. between the nervous ring and the mouth, is a large 

 globose muscular sac, on its exterior sides having a wonderful 

 system of powerful muscles leading to different parts of the 



