■2 | ; ; INTRODUCTION. 
anterior lobes of the liver are comparatively very small, 
while the posterior lobe is correspondingly large ; and to 
the whole there is but a single duct. 
Chapter v. — observations on the tissues of the 
digestive apparatus. 
The mucous membrane of the alimentary canal is 
usually smooth throughout. In the stomach it frequently 
presents a number of transverse folds, corresponding to 
the contractions which produce the sacculated appearance 
of the organ ; and in several species of different genera 
it presents a few longitudinal rugae, as in Limax varie- 
<jata, Bulimus fasciatus, Helix cxolcta, etc. In its 
whole extent it is formed of a columnar epithelium and 
a nucleolated-nucleated basement membrane. The col 
umnar cells of the epithelium arc long and pyramidal 
the upper part or base being broad, and the attached ex 
tivmity very narrow. They are filled with a very fine 
indistinct, granular matter, intermingled with coarser 
highly reflective granules. Each contains an oval, gran- 
ular nucleus, with a minute nucleolus. 
The muscular investment of the intestinal canal is 
strongest upon the stomach and rectum. In Vaginulus, 
Pupa incana, etc. it is strong and shining upon the sto- 
mach. It consists of two layers, an internal transverse 
and an external longitudinal. They are both composed 
of white, shining, strap-shaped bands, with the extremities 
pointed and closely adapted to each other. None of 
