83 
bordered apparently by two thick lips, but this could not be very 
plainly seen. This opening seems to lead to an obscure alimentary 
canal. Further back than this is a still larger median sucker. The 
whole surface of the body is covered with small hook like spines. 
Down each side in some specimens a branched bead-like structure 
can be made out. 
The sporocyst (see Plate, figs. A and B) is oval, pointed at one 
extremity, with two conspicuous black eyes, the other end is rounded 
and the whole body is covered with cilia which are constantly in 
motion in the living animal. The sporocyst may contain three 
different elements, (1) spherical masses full of smaller spheres, (2) 
the same but with two of these masses in one envelope, (3) minute 
sporocysts exactly like itself and containing small spheres. 
These are not generally all present at the same time, the first 
two being found together without any of the minute sporocysts 
which latter are usually found alone almost filling the body of the 
parent, one or two of the large double spherical bodies being some- 
times present. The small sporocysts burst out of the side of the 
parent and stream out, moving about slowly, and soon get separated 
from one another. 
Apparently there is nothing special about the shells of the 
cockles that contain these parasites. One measured 44 mm. across, 
its organs seemed to be in a healthy condition but were not 
investigated closely. 
Sections of an affected foot were cut and stained but the sections 
were not successful so far as the parasite is concerned. The cysts 
showed a thick wall staining deeply. The tissues of the foot round 
about the cyst were greatly modified, staining much more deeply 
than the natural tissues, giving signs of having arisen through 
considerable cell multiplication. 
So far I have not discovered a cercaria stage. The specimens 
do not appear to contain them. Possibly it may not be the right 
time of year for them. I hope also to be able to discover the adult 
stage in some fish or sea bird. 
The following is a table showing the numbers of sporocysts in 
20 cockles, the intestines and livers of which were carefully examined. 
It will be seen that 6 had apparently no worms in them nor 
sporocysts, 10 had no worms in the foot but had sporocysts, and 
4 had both. Of the 14 cases in w^hich sporocysts were present, 
