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AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



and on the visceral hump, where it is so thin and transparent 

 that many of the internal organs can be seen through it. Else- 

 where the surface of the body is corrugated. The skin is very 

 glandular and secretes the characteristic slime. 



The skin consists of an epidermis made up of a single layer of 

 cells, and a connective tissue dermis, closely united with under- 

 lying muscular tissue. The epidermal cells are flat on the visceral 



Fig. 35. DIGESTIVE ORGANS AND NERVOUS SYSTEM or SNAIL. A, General 

 view ; B, left side of stomach, &c. ; C and D, side and hind views of 

 buccal mass; f, foot; t, tentacle; m, mouth; b.m, buccal mass; r.s, 

 radular sac ; ce, gullet ; cr, crop ; st, stomach ; i, intestine ; r, rectum ; 

 a, anus; s.gl, salivary glands; s.d, salivary ducts; LI, Lr, left and 

 right lobes of digestive gland; l.b.d, r.b.d, ducts of ditto; c.g, cerebral 

 ganglion ; v.g, ventral ganglionic mass ; b.g, buccal ganglion ; t.n, 

 tentacular nerve; b.n, buccal nerve; o.t, hermaphrodite gland; h.d, 

 hermaphrodite duct ; g, place from which genitals have been cut away. 



hump, cylindrical elsewhere. Many of them constitute uni- 

 cellular mucous and pigment glands, while few-celled pigment 

 and calcareous glands are also present. These various glands 

 project into the dermis, which is also traversed by muscle-fibres, 

 blood-spaces, and nerves. 



