CAPILLARIES IN INTEGUMENT OF MEDICINAL LEECH. 305 
perforations which are irregularly placed but tend to a dis- 
position such as that seen in the figure. These perforations 
are the openings of the unicellular glands. Frequently two 
such apertures and sometimes three are placed closely side 
by side. 
Columnar Cells . — When the epithelium is carefully ex- 
amined by means of very thin sections and by teazing, it is 
found that the columnar cells which form the stratum sub- 
jacent to the cuticle have not a simple columnar form but 
are T-shaped or rather mallet- shaped (fig. 1). The broad 
expanded portion, the head ” of the mallet, forms with its 
fellows a complete mosaic (fig. 6) immediately underlying 
the cuticle, whilst the handles ” of the mallets are arranged 
side by side so as to leave a certain amount of space between 
neighbouring handles (fig. 3). Into these spaces pro- 
cesses of the connective tissue here and there make their 
way, these processes being outgrowths of the pigmented 
vaso-fibrous tissue which pervades the whole body of the 
Leech (fig. 3 pg). The variously coloured spots of the 
Leech’s integument are produced by modifications of this 
tissue, and the amount of it which interlocks with the epi- 
thelial cells varies from point to point according to the 
pattern of the Leech’s colouring. 
Columnar cells which have been teased out, after macera- 
tion of the Leech in potassium bichromate, show the ex- 
panded head ” having a finely granular or sometimes 
vacuolated structure, whilst the “handle” appears very nearly 
homogeneous (fig. 1). I have not been able by staining 
agents to show a nucleus in any part of the cell. The whole 
of the “ handle ” takes the staining rather freely, and it is 
possible that it consists chiefly or entirely of nucleus. 
When a detached flake of epithelium, which has been 
stained by picro-carmine, is looked at from above, the appear- 
ances represented in figs. 6, 7, 8, 9 are obtained. A complete 
mosaic of polygonal cells is seen, in some of which are dark, 
that is to say, well-stained bodies, ^vhich look like nuclei. In 
others of the polygonal area there are no such darkly-stained 
bodies, but only fainter indications of a differentiation. The 
result is that the cells with darkly-stained bodies in them 
are arranged in irregular groups (fig. 6). The darkly-stained 
bodies prove upon further examination to be 7iot ordinary 
nuclei, but the “ handles ” or depending portions of the 
epithelial cells. 
In such fiake-like preparations some of the cells are seen 
to be perforated by one or by two circular holes. These arc 
the passages for the ducts of the unicellular glands. 
