436 
Melinda cognat a Meigen 
however, one can see through the transparent tissues the flattened or folded 
empty egg-shell lying in the posterior end of the mantle cavity, and, in the 
posterior end of the kidney can be seen the moving mouth-parts of the larva, 
these appearing as a small black spot. The rest of the larva is difficult to see 
but sometimes its posterior end is visible when it projects from the kidney into 
the mantle cavity (L. PI. XXIII, fig. 3). Within the kidney, the larva passes 
through its first moult, the excuvia, including the mouth-parts of the first 
stage, remaining by its side. 
During the second stage it grows rapidly, enlarges the kidney and lies in the 
mantle cavity with its ventral side toward the shell of the snail. It thus 
assumes a curved position, its ventral side being convex and following the 
curve of the shell, but the spiracles always remain in communication with the 
air, being directed towards the pneumostomeof the mantle cavity (L. PI. XXIII. 
fig. 1). The snail may still retain its activity and may be seen moving about 
slowly, but more frequently it fixes itself to a plant and lies retracted in its shell. 
The larva now moults a second time and passes to its third and final stage. 
It becomes very active and voracious, entirely destroys the kidney, attacks 
the liver, and its effect upon the host becomes very distinct. The snail no 
longer moves about but is always retracted within its shell which is sometimes 
fixed upon a plant but more frequently lies loose upon the ground. 
The larva grows rapidly and soon occupies the whole length of the mantle 
cavity whilst it projects its posterior end through the pneumostome into the 
external air (L. PI. XXIII, fig. 6). 
In the meanwhile the walls of the mantle cavity have become shrunken 
and have presumably ceased to function, although the snail is not yet dead as 
is shown by small contractions of the foot and of the region surrounding the 
pneumostome. 
All the organs of the host are attacked in turn. The liver, which is very 
fragile, is destroyed, the alimentary canal is perforated, and the snail ulti¬ 
mately dies before the larva is full grown. 
One knows with what rapidity a snail decomposes after death. Within two 
days of its ceasing to show any movements the animal is transformed into a 
strongly smelling decomposed liquid mass forming the final meal of the 
parasite which thus ends by being saprophagous. 
As previously mentioned, while feeding upon the living snail, ‘the larva lies 
with its ventral side towards the shell and assumes a curve by which that side 
is convex, and it is interesting to note that this curve is retained even when the 
larva is lying free in the putrefying remains of the host. 
As the food supply is exhausted, the larva works its way into the upper 
whorl of the shell which it completely occupies. During the whole of the 
saprophagous period, the posterior spiracles of the larva remain in communi¬ 
cation with the external air. 
If one of the shells containing the larva in this stage is broken, and its 
contents emptied into a dish with some water, a transparent tube, many times 
