202 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
passes at first forwards and downwards, then comes round 
into the mass of the gland. A great number of smaller 
lateral ductules open into these principal ducts, and on 
them are arranged in clusters the secreting alveoli of the 
gland. 
The epithelium of the stomach passes gradually into 
that of the ductules of the gland. The tricuspid body 
disappears ; the long spindle cells become shorter, and a 
corresponding decrease in length of the cilia takes place. 
But the epithelium of the ductules (fig. 17, Pl. IIL.) always 
consists of spindle cells carrying cilia, and their walls are 
thrown into slight longitudinal folds; at the passage of 
the lumen of the ductule into that of a secreting alveolus 
a rapid transition from this ciliated epithelium into that 
characteristic of the alveoli takes place (fig. 15, Pl. II1.). 
The fixation and subsequent treatment of the. digestive 
gland, so as to exhibit the nature of the secretory epithe- 
hum, is difficult, but good results are to be obtained by 
McMunn’s method. A very small piece of the gland is 
rapidly removed from the living animal, and at once put into 
a 20% solution of commercial formaldehyde in water. The 
tissue 1s allowed to remain in this for about 24 hours, and 
is then transferred to 70% spirit and dehydrated, embedded 
and cut in the ordinary way. The sections are stained 
with Mayer’s glychaemalum and eosin, or with Heiden- 
hain’s iron haematoxylin. With fixing reagents of less 
penetrative power the epithelium breaks up in the process. 
The lumen of the alveolus is always a very restricted one, 
and is usually cruciform in transverse section. The spindle 
cells becomes cubical and the cilia disappear (fig. 15, Pl. 
IIf.). Then the cubical epithelium becomes replaced by 
four groups of large club-shaped cells (fig. 16, Pl. III.). In 
tangential sections of the alveolus these cells, which are 
then cut transversely, have very definite polygonal out- 
