INTRODUCTORY HISTOLOGICAL STUDY 
2 9 
angles to the free surface (: i.e a vertical section of the epithelium) 
or is parallel with the free surface (i.e., either a tangential section 
of the epithelium or a surface mount). Keep in mind the fact 
that in order to understand the shape and arrangement of the 
cells it is necessary to study them from both aspects. In case of a 
vertical section note the sharp delimitation of the epithelium from 
the connective tissue upon which it rests. Consider whether the 
arrangement is in one layer (simple epithelium) or more than one 
(stratified epithelium) ; what the prevailing shape of the cells is 
(squamous, cuboidal, or columnar) ; and whether there are indica¬ 
tions of cells with special functions (protective, secretory, or 
motile). Record by suitable drawings on a sufficiently large scale 
to show the parts of the individual cells, as well as their arrangement. 
The following preparations (Lab. SI. Coll.) are suggested for 
the study of epithelial structures although others equally good may 
be added or substituted. 
1. Sections of the gall bladder of Necturus showing a lining of 
simple cuboidal epithelium seen mainly in vertical section, though 
limited regions may be cut tangentially. 
2. Transverse sections through the stomach and gastric 
diverticula of a grasshopper showing in vertical section a lining of 
simple columnar epithelium. 
3. Transverse sections through the intestine of some lower 
vertebrate (e.g., Necturus) showing in vertical section a lining 
of simple columnar epithelium, with numerous secretory cells 
(mucous cells) among the cells of more general character; and an 
outer covering (visceral peritoneal layer or serosa) of simple 
squamous epithelium also in vertical section. 
4. Sections through the coiled oviduct of a mammal showing a 
simple ciliated columnar epithelium, mainly in vertical section. 
5. Surface mounts of the mesentery showing the simple 
squamous epithelium of a serous membrane. 
6. Transverse sections of the oesophagus of a lungless sala¬ 
mander (e.g., Desmognathus or Eurycea) showing in vertical sec¬ 
tion a stratified columnar epithelial lining only two cells thick, 
with both secretory (mucous) and motile (ciliated) cells. 
7. Vertical and tangential sections through the skin of young 
salamander larvae (e.g., Desmognathus or Eurycea) showing an 
