126 
muscle layers of the body-wall. They suddenly become thinner 
near the basement membrane and have then a diameter of only 
4 i^i. Here they also begin to coil, with the result that it is quite 
difficult to trace them and follow them from section to section. 
On account of the formalin preservation used, the epidermis together 
with the basement membrane has almost everywhere in the middle 
of the body come loose from the muscularis (cf. Plate IV, Figs. 
25—28). Therefore, it is very difficult to find the correct places where 
these efferent duets fit into the epithelium. However, somewhat 
thicker canals than those of the efferent ductuli from giand cells 
embedded in the parenchyma have been distinguished in some 
cases in the basement membrane and the epidermis, and these 
may possibly represent the end-parts of the exeretory canals. It 
might be mentioned that exits for the exeretory canals have not 
been observed to date in the Polyclads (see for instance Lang’s 
description of the exeretory system of Thysanozoon, p. 166). 
The outline of the large exeretory canals is distinet and there 
is a delicate membrane stained with hematoxylin. This marked 
membrane may of course also be visible from the flat side. Nuclei 
of the Wall of the canals oceur only here and there and with very 
large intervening spaces. On account of the preservation the plasma 
lining of the canals appears indistinet and it is often impossible 
to discern it. On the other hånd, the fine cilia found projecting 
into the lumen of the canals can easily be observed. Judging also 
from the exits of the cilia, the plasmatic wall is very thin. In this 
plasmatic wall of the canal one may occasionally see scattered 
gatherings of light grey-blue granules which perhaps represent 
exeretory products. 
I should attribute the splendid development of the exeretory 
system in this species to the faet that the muscularis present in 
the parenchyma is so robust. This rather compact musculature has 
inereased the demands on the metabolic processes of the body, 
which has necessitated a better organized exeretory system than 
that usual for the Polyclads. It would probably not be quite unreas- 
onable to suppose that a water current in these canals would be 
of importance for the supply of oxygen to this musculature. 
Digestive system: Regarding pharynx, I shall only refer 
to Plate III, Fig. 20 and point out that the pharyngeal fold running 
