252 
[April, 
s ca*_e foi pupating, it joins the two pieces so closely together, as to 
lei it wateitight, but before that time the openings at the ends are 
generally so wide that the water cannot be kept out. 1 am, however, 
posed to agiee vith Reaumur’s statement that the larva can control 
. e °f v ater to its case, and probably this is regulated by 
s lequiiemcnts in the matter of respiration, and must be managed 
by enlarging or contracting the orifice at either end. 
A\ hen a lan a makes use of M yosoiis, after selecting the end of a 
leaf, and detaching a piece of proper length by a semicircular cut, it 
floats off upon it towards the end of another leaf; there it either 
on the upper surface, and turns over the piece it is carrying 
so as to form its new roof, or else carries it underneath and fastens it 
there as its new floor ; either way, after fastening the edges of the 
detached piece in place, the larva seems to be at leisure in cutting out 
v hat is needed from the leaf to complete its case, eating away the 
surroundings, and not merely making a cut ; the cavity between the 
roof and the floor seems formed by having one of them broader in the 
first instance than the other, so that when the edges are joined, there 
is necessarily a bulging out of the broader piece. 
When Sparganium is the material, the case is of a narrower and 
more elongated form, the floor being the flatter side, and thus shorter 
than the roof, which is arranged so that the keeled surface of the 
leaf is outside, and the thin side-edges drawn inwards, and thus made 
to help in the formation of the cavity. Not unfrequently the case is 
ormed of two sorts of leaf, for a larva is not particular to have its 
case all of the same material ; apparently in its growth between two 
moults it changes only one-half of its case at a time, whereas after a 
moult it sometimes makes a new case entirely ; when, therefore, it 
wants only a new roof or a new floor, it takes it from a suitable 
plant nearest at hand, cutting the new piece a little larger than its 
predecessor, and m this way, by changing the top and bottom 
alternately, it soon brings a small case up to a good size. 
. . ° n Jun / llth ’ 1 110ticed a larva Poking as if about to moult, and 
isolated it for observation : the moult took place on 13th ; after the 
skm burst at the neck, the old head-cover first fell off, and then the 
(almost colourless) larva began slowly to advance into the water out 
of its case until nearly exposed, then it stopped still for about ten 
minutes, when suddenly the hinder segments were set free with an 
effort that sent the case adrift, while the larva remained quite naked 
in the water : I secured the abandoned case, and opening it found the 
cast flaccid skm— not shrivelled up— but held out at full length by 
silk threads along the ventral region. b J 
