THE STRUCTURE OF CRYPTOGONIMUS 
529 
I have made every effort to determine whether the usual flame 
cells and capillaries are present here or not. Xo traces of either 
have been seen. This negative evidence does not sufl^ice fully 
to demonstrate the absence of flame cells but the excretory cap- 
illaries and tubes of trematodes even of quite immature stages 
are usually very distinct structures and readily recognized so that 
it seems as if they would have been seen in this species if they 
are in existence. It seems most likely that they are not developed 
at all and that if the flame cells are in existence their products 
are merely conveyed by way of spaces among the cells to the 
nearest point in the system of excretory cavities. 
In all adult cases examined, whether of living worms or of total 
mounts or sections, the cavities of the excretory apparatus were 
found entirely empty. As already stated, contractions of the 
wall and the escape of excretorj^ substance were observed. This 
was in marked contrast with the conditions in the encysted stage, 
in which (see fig. 7) the excretory apparatus is somewhat as in 
the adult, except for the confluence of the anterior cavities at the 
front level. In this stage the cavities were filled with small 
very highly refractive globules. Each showed a very refractive 
surface contour and clear interior like an oil droplet. They were 
of different sizes and each kept its identity. I have found a sim- 
ilar condition in Clinostomum where in encysted worms the ex- 
cretory cavities were filled with such granules which were at once 
discharged on liberation of the worm from the cyst. It would 
appear from these facts that the process is one of storage during 
encystment as a mode of disposing of the waste products pending 
the liberation of the worm. 
It is seen from this account that the excretory system is much 
less differentiated here than is usual in flat worms. I am inclined 
to regard this condition as an arrest in the embryonic develop- 
ment of the system, while the other systems of the animal have 
gone on in the usual manner. In casting about for a cause to 
which to attribute the supposed arrest the most probable fact 
is the small size of the animal. The amount of waste chemical 
material must be very small, and such a very elaborate and exten- 
sive apparatus for excretion as the one found for instance in 
