ALIMKNTAR Y SYSTEM — PLECTON. 
2 8 "2 
Ijeliiiul the shield still retain a YCiy considerable twist, equal to 
about one and a half s[)iral turns and recalling the similar twisting 
exhibited by the internal organs of 
/iitlimiiiHS, and yet, excei)t the lateral 
position of the organic orifices, there 
are no external evidences of their 
spirally coiled viscera, and it forms 
removed, showing the spirally twisted . ^ i ,• r ,i 
digestive gland and intestinal tract, X 2. Un6*Xp0Ct0l.l COlTObOrtltlOU 01 tllO 
former i)Ossession of a spiral shell by these groups. 
The Intestinal canal may he conveniently divided into two sections, 
an anterior section, the Plecton, which is usually more or less com- 
plexly convoluted, and a straighter terminal one, the Rectum. 
The Plecton (-AeKToc, twisted or twined) originates upon the 
ventral side of the stomach, fnmi which it is sometimes separated by 
a sort of valve, and in the herbivorous 
and omnivorous species is often very 
long and complexly convoluted, a feature 
which has arisen chietly by the elonga- 
tion of the ])rimitively straight and 
simple canal; the coiling exhibited is, 
however, never continuous in one direc- 
tion, like a watch-spring, hut is reversed 
from time to time, so that the tracts 
cimsidered as convex are ])ractically 
e([ualled by others bent in an oi)posite 
direction and forming what is known as a 
“reversed spiral,” an arrangement which 
always takes })lace when a lengthening 
hod)' with fixed ends is confineil within 
a limited .sj)ace. 
'I'he Plecton, though continuing the 
digestive processes set up by the stomach and also receiving the 
secretions of the digestive gland in those species not i)ossessing the 
crystalline style, is chiefly absorptive in function, this jn'oeess being 
facilitated by the development on the ventral side of the intestinal 
tube, es])ecially in the earlier i)art of its course, of a strong inhdding 
(jf its walls, which greatly increases the al)sorptive surface and forms 
what is known as the T)q)hlosole. This absorption of the nutritive 
products of digestion from the alimentary tract is not accomplished 
P'lG. 503. — Alimentary tract of Sue- 
cinco. dedans Kisso, x 5, Exminster 
Marshes, Devon, collected by Mrs. 
Smith, showing the character of the 
plectonic and rectal tracts. 
h.b. buccal bulb; cp. oesophagus; 
c. crop, blending with stomach st. ; 
p. plecton or coiled intestine ; r. 
rectum. 
