Haswett—A Monograph of the Temnocephalee. 117 
single nucleus, of a diameter of about 023 mm., which when stained with heematoxylin 
shows a large spherical stained centre with a number of much smaller rounded bodies, 
also intensely stained, arranged round it ina single layer, and with a scanty intra-nuclear 
achromatin network, between the meshes of which and adhering to the threads are 
irregular minute particles which have the appearance of flocculent matter precipitated 
from a fluid. These cells are devoid of any enclosing membrane and, usually, 
though not invariably, have a number of processes. The canal breaks up on entering 
the cell into a number of capillary channels (PI. x1. figs. 2 and 3) which ramify richly 
throughout the protoplasm in all directions. In other cases small vessels run round 
the periphery of the excretory cell and send minute capillary branches into its 
substance. I have not been able, after often-repeated and careful search, to find 
‘“Wimperflammen” in the course of these intracellular channels, and though, taking 
into account what has been described in regard to the terminal cell, it seemed not 
improbable a priori that those structures should be present, I think I have made 
fairly certain that they are not. 
Cells in most respects similar to these, of similar size, with nuclei of precisely 
similar character, and with coarsely fibrous protoplasm having a radiate arrangement 
but apparently devoid of canals, are to be found here and there ; a set of these always 
oceurs, arranged with the greatest regularity, between the bases of the tentacles 
and the pharynx; they are frequently perforated by dorsi-ventral strands of the 
parenchyma muscle. 
It will be seen from the above that the entire excretory system of Zesenocephala 
(with the exception perhaps of some of the fine capillaries), is intracellular, and that 
the entire number of cells in the interior of which the system les is very limited. 
A part at least of the system of larger trunks has a wall formed of a branched 
extension of the subterminal cell and of one or two others; a part doubtless is formed 
by extension of the renal cells ; what share those cells severally take in forming the 
trunks could only be decided by a detailed investigation of the development of the 
system. 
The remarkable result also follows that structures which appear to correspond 
to flame-cells of other flat-worms are not here of the character of cells at all—a large 
number of ciliary flames being present within the substance of a single large cell. 
Another set of cells which are probably appended to the excretory system, 
though positive evidence of this is wanting, are much fewer in number than those 

as much as ‘16 mm. in diameter, with 
nuclei about ‘03mm. They differ from the excretory cells in the effect of staining 
agents on their protoplasm, in the larger size of their nuclei, in the presence of a 
just described, and usually of even larger size 
