No.3.] VESICLE OF HIRUDO MEDICINALIS. 487 
representing the seventeenth section of the series. The lumen 
of the terminal duct (¢.¢.), part of the terminal vesicle (¢.v.), and 
the exterior are filled out with black ink in the drawings. 
In Figs. 1 and 2 the terminal duct is cut only in a few places. 
In the middle and close to the terminal vesicle we see longi- 
tudinal sections through circular muscle-cells (s.#.) as we have 
to expect in a surface section. Figs. 3 and 4 show part of the 
lumen of the terminal duct in the middle (black), and now we 
meet longitudinal sections through the sphincter muscle-cells, 
close to the epidermis (e). In the places where (in Figs. 1 and 
2) we saw longitudinal sections through sphincter muscle-cells, 
we find here cross sections. In Figs. 5 and 6 the sections of 
sphincter muscle-cells close to the epidermis shorten up, until, 
in Figs. 7, 8, and 9, we find all the sphincter muscle-cells in 
cross sections at the two sides of the terminal duct now show- 
ing its lumen entirely. 
In the following sections the same pictures are repeated, only 
in reversed way. Fig. 10 (17) gives a view of section 17 of 
the series which would almost exactly correspond to Fig. 3. 
If H. Bolsius suggests that I mistook body muscle-cells for 
sphincter muscle-cells he must take me for a very superficial 
observer. The difference in size and structure is so great 
between those two kinds of muscle-cells that nobody could 
mistake one for the other. The body muscle-cells are, on the 
one hand, four times as large as the sphincter muscle-cells ; 
and, on the other hand, the body muscle-cells are striped longi- 
tudinally and show the fibrils deeply stained; whereas the 
sphincter muscle-cells are smooth and are much less stained. 
MARINE BIOLOGICAL LABORATORY, Woop’s HOLL, 
August 9, 1894. 
