450 
Second Report of Experiments of the 
surface of the snail, aided in this by the contraction of the 
body of the embryo, which is slowly drawn up and then 
rapidly extended. As the papilla sinks further and further 
into the soft tissues, acting as a wedge in forcing the neigh- 
bouring cells apart, it becomes long and narrow, and the 
bulbous enlargement at its base disappears. The papilla has 
now four or five times its ordinary length, and I have observed 
it penetrate between the columnar epithelial cells of a snail's 
foot to the depth of '022 mm. (See Fig. 2.) I could never observe 
an embryo actually enter the snail in this way, the tissue of the 
foot being probably too unyielding, at least when pressed on 
by a cover-glass. The embryo withdrew its papilla, and 
searching for a softer place, at once recommenced its boring 
operations. I have, however, found embryos in the connective- 
tissue of the foot in other specimens of Limnceiis, and these had 
evidently forced their way in by boring in the manner described. 
The layer of cuticular cells is shed, but the embryos do not die 
at once, notwithstanding that such a situation is unfavourable 
to further development. 
A differentiation in the tissue of the head-papilla is visible 
in the form of a delicate rod-like structure occupying the axis, 
not distinct enough to be called a spine, though it possesses con- 
siderable rigidity. It is particularly evident in preparations of 
embryos killed with osmic acid and stained with picro- 
carmine. 
Leuckart states in the same paper that he received a number 
of specimens of L. tnmcatulus, gathered from the banks of the 
Main, and at once examined these for larval trematodes. He 
found three different kinds of rediae. One of these contained 
tail-less distome-larvae, and notwithstanding that the redia& 
differ in certain respects from those found in his infection 
experiments (they have no lateral processes), he thinks he is 
justified by the characters of the included larva? in considering 
this form to belong to the liver-fluke, at any rate until further 
results are obtained. His reasons are : 1, the larvae included 
in the rediae are tail-less forms, which may indicate that they 
are not destined to leave the snail in which the redia is found ; 
2, the surface of the larvae is beset with spines ; 3, the relative 
sizes of the oral and ventral suckers are much the same as in 
the liver-fluke. He was unable to test the matter by feeding 
a sheep with these tail-less larvae, as he found them in only 
one of the snails. 
In endeavouring to refer the young larvae of Distomidcc to 
their respective adult forms, we have but few characters upon 
which we can rely, as so many of the most conspicuous charac- 
ters of the young are only transitory larval peculiarities, whilst 
