ALIMENTAR Y SYSTEM— TRIODROMA. 
'J84 
'I’he Re^tatheca (rccfd, straiglit ; t/iecu, a sheath), a reiiiarkal)le 
hliud (Hvertieuluiu, arises about inidway in tlie course of the rectum 
and extends backwards above tlie stomach in certain of our nude 
species, but its signiticance or function is unknown, altliough in Birds 
analogous structures have been correlated with the function of 
digesting chitin and cellulose, and it 
is probable that this is also its 
function in slugs, as fungi, which are 
mainly composed of cellulose, are a 
favourite food with the species pos- 
sessing the cmcuni. A7'io)i ate/' is 
also stated by Simroth to possess a 
cylindrical ca'cum, situate behind the 
hepatic ducts, which he regards as 
probably possessing special digestive 
power, and thus may be analogous in 
function to the Rectatheca. 
Our British species may be pro- 
visionally sei)arated into three groups, 
viz. : — Dichodroma, Triodroma and 
Rentadroma, which are based upon the 
number of tracts the intestinal canal 
exhibits, although the tracts in all the 
groups vary greatly, not only in their 
length, but in the number and direction of their subsidiary flexures. 
The 'I'riodrom.v (rpt-, three; ^/)o/ro«, a tract), which is the prevailing 
type of intestinal convolution in our British .species, po.s.sesses only 
three chief intestinal tracts beyond the stomach, the first loop being 
4 * 
Fio. 507. — Alimentary tract of Kclix lapicida L., X 4, as exemplifying the section Triodroma. 
always ventral to the stomach and having a forward course, which 
is considerably varied in detail in the different s^iecies, but usually 
ascending above the oesophageal tract where the first anterior loop is 
formed, which in the Euthyneura is held in position by the ceiihalic 
branch of the aorta, afterwards passing more or less diagonally back- 
wards and there bending forward to the rectum. 
Fir.. 500. — Alimentary tract of Lintax 
/Ia7'us L., showing the large intestinal 
cceciim or Rectatheca, x 2. 
buccal bulb ; c.^. cerebral ganglia ; 
cr. crop, blendifig with the stomach st. ; 
a. anus; c.ui. intestinal c«x:cum or 
Rectatheca. 
