ao 



204 THE ORGANIZATION 



Snail is the forepart of its 

 body, including its head, (t, t 1 ,) 

 the muscular disc, or foot (m to 

 ac) upon which it creeps, and 

 that portion which lies imme- 

 diately above the latter and in- 

 cludes the stomach, (st,) the 

 bulk of the nervous system, (sg; 

 c, g; n, ng,) and the emptying 

 conduits of the reproductive or- 

 gan (or 1 , o). Within the shell are included the posterior half 

 of the digestive system, the reproductive organ, (ov,) the heart, 

 (A, A 1 ,) and the lung (pv). That part of the body which is 

 usually extended from the shell (sh) has an elongated spindle 

 shape, and is flattened upon the lower side so as to form the 

 creeping disc. At one end, which is the head, it is truncated, i. e., 

 as if cut straight across. The head has four feelers, of which 

 the upper pair (t) are the longer, and have each an eye-spot (e) 

 at the end. The lower pair (t l ) are mere tactile organs. 



The mouth (m) is situated on the lower side of the body, and 

 just behind the truncate end. From it the stomach (st) extends 

 directly backwards for about two thirds the length of the body, 

 and then narrowing into an intestine, with varying convolutions, 

 passes within the spire of the shell, (sh,) and bending upward, 

 forward, and considerably to the right, comes to a termination 

 (m 1 ) near the upper right edge of the aperture of the latter. 



The circulatory system consists of a heart (A, A 1 ) with two 

 cavities, one for receiving and the other for the distribution of 



Fig. 123. A foreshortened, diagramic view of fig. 122. Ip, the lip at the 

 anterior border of the mouth of the shell; st, the stomach; ac, the abdominal 

 cavity; h, the auricle of the heart; h 1 , the ventricle of the heart; hv, the vein 

 which brings the blood from behind to h ; pv, the pulmonic vein ; ao, the aorta 

 coming forward; ao 1 , the aorta which branches at ao a , in the region of the liver 

 and reproductive organs ; sg, the super-oesophageal nervous ganglions ; g, the 

 sub-oesophageal ganglions ; g\ the inferior edge of the nervous collar ; c, the 

 lateral threads of the nervous collar; ng, the nerve which branches in the foot; 

 n, transverse branch from nq ; nv, the reproductive organ. Original. 



