SPECIAL ANATOMY. 57 



this portion and the mucous layer is placed the rudimentary testa 

 (Fig. 5, 6). In Tebennophorus it is inflected inwards (Fig. 6, 5) be- 

 neath the anterior portion of the mantle, to form the parietes of the 

 pulmonary cavity. Its transverse fibres predominate within the eye- 

 peduiicles, its longitudinal fibres, in the exterior pulmonary parietes of 



rig. 7. 



Fig. 7, disposition of the tegumenta in Helix, Bulimus, etc. The references are the same as in Figa. 

 6 and 6, except 1 *, which is the collar. 



the testaceous genera, and especially accumulate on the outside of and 

 parallel to the rectum, so as to serve as an efficient agent in the retraction 

 of the collar, and an aid in the expulsion of matters from the rectum. 



Interior to the musculo-mucous investment of the body is a second 

 covering (Figs. 5, 6, 7, 3), which may be considered as a sort of perito- 

 neum. It is a muscular membrane, and encloses the digestive and 

 generative apparatus. It is usually pretty closely attached to the outer 

 tegument, except in Tebennophorus Caroliniensis, in which the two are 

 separated in all parts of the body, except above the pedal disk, where 

 they are firmly blended together, as in all Gasteropoda. It forms the 

 partition or diaphragm between the visceral and pulmonary cavities. 

 This membrane is composed of transverse and longitudinal, unstriped, 

 nuclear fibres, and is the origin of the especial retractor muscles of 

 different organs. 



OP THE DIGESTIVE APPARATUS. 



LIMAX. The orifice of the mouth is bounded by a pair of contractile 

 lips, is situated at the anterior part of the head, and opens into the 

 cavity of the buccal body. When the latter is retracted by its peculiar 

 muscle, the oral orifice becomes lengthened into a canal by the inversion 

 of a portion of the external integument. 



The buccal body is an irregularly oval-shaped, muscular organ, re- 



