22 NATURE 
it was connected with the artificial conditions in which 
my larve were reared, I do not know. 
‘Once the larva leaves the water it crawls about 
very actively, seeking a suitable place to enter the 
earth. If left to itself it usually selected a stone and 
burrowed underneath it, but I found that if I made 
an artificial burrow—with a pencil, for instance—the 
larva could be made to crawl into this, and as a 
rule would make its “cell” in it. By making such 
a burrow against the glass side of a box filled with 
earth, I was able to watch the process of the forma- 
tion of the pupal cell. 
Once the larva has entered and adopted the burrow, 
it straightway begins to prepare its cell, and this is 
done by enlarging part of the burrow. The jaws are 
now used for transporting pellets of soil from one 
position to another, and for breaking up the pellets 
into their separate particles. | Very little earth is 
actually pushed into the unused part of the burrow, 
the cell being formed almost entirely by breaking up 
the pellets of soil and battering the fine particles 
against the sides. The vertex of the head is the 
main battering-ram, but the larva, which during the 
whole precess of making the cell lies with its tail 
bent over its head, also flattens out the earth with 
its body. 
The actual making of the cell occupies about twelve 
hours, and during that time the larva does not rest 
for a moment. At the end of that time it is appar- 
ently tired out, and rests in any position, often 
stretched across the cell, its head pressed against one 
side and its curved body against the other. It thus 
rests for about twenty-four hours, after which it bends 
its tail underneath it and usually adopts a sitting-up 
position—reminding one of Tenniel’s illustration in 
“Alice in Wonderland” of the caterpillar sitting on 
the mushroom. It is, however, very restless, and 
frequently changes its position, tossing from side to 
side. 
The pupa appears, after the larva has been thus 
resting for a fortnight or more, by the larval skin 
splitting along the back and being cast off at the tail 
end. On its back are to be seen a number of short 
projecting spines, and Lyonnet suggested in the case 
of another pupa, similarly though better equipped, 
that these are for the purpose of raising it off the 
damp soil of the cell. This may be true, but in my 
experience the pupa most usually lies, so to speak, 
on its face rather than on its back. 
The pupal stage lasts about three weeks, and the 
only change noticeable during that time is a slight 
pigmentation of what is at first a perfectly white 
pupa. At the end of the pupal stage the skin ruptures 
along the back, and the perfect insect comes forth at 
first white and soft, but in the course of two or three 
days it assumes its normal coloration, and after a 
longer period its normal hardness. After a week or 
so it makes its way out of the punal cell by biting 
and scraping, and at once goes to the water. 
In its native haunts it spends most of its time 
amongst the stones and mud at the bottom, occasion- 
ally coming up to renew its air-supply, and in my 
tubs also it was seldom to be seen. 
With regard to its winter habits, it apparently 
buries itself at the bottom of the loch as soon as 
the cold weather begins, and sleeps until the following 
spring. In my tubs it disappeared completely in 
October or November, burrowing deep into the soft 
oozy mud at the bottom, and there it remained until 
the following March. During all this time the meta- 
bolic processes must be practically at a standstill, as 
otherwise the insect would require to renew its air- 
suvnly at frequent intervals. 
Having now outlined the life-history of this type 
of the swimming carnivorous water-beetles, I will take 
No, 2288, VOL. a2] 
[SEPTEMBER 4, 1913 
an example of the other group, and the one I have 
chosen goes by the name of Hydrocharis carabéides. 
There is only one species of Hydrogharis in the British 
Islands, and it is practically confined to the south- 
east of England, only very occasionally having been 
found anywhere else in the country. It inhabits stag- 
nant ponds and drains, and is not uncommon in a few . 
places in Surrey, Essex, and Middlesex. 
I began to experiment with it five years ago in the 
north-east of Ireland, having obtained my specimens 
from Surrey. Each year I obtained eggs, reared the 
larvee, and renewed and increased my stock, so that 
it is obviously not the climate of north-eastern Ireland 
which prevents this species from being a native there. 
The conditions in my tubs were just such as are to 
be found in any pond or drain in the country, and 
apparently the only reason why this species is con- 
fined to the south-east of England is that competing 
species prevent it from extending its range. 
Whereas Dytiscus lays its eggs singly in holes 
pierced by it in the living vegetation, Hydrocharis 
builds an elaborate silken cocoon which floats in the 
water, and in which about fifty eggs are deposited. 
The spinning of the cocoon is a wonderful process. 
The beetle carries on its underside a film of air, which 
is part of its supply for breathing. The cocoon is 
actually spun on a part of this film of air, which is 
then detached from the rest of the film as a bubble 
enclosed in silk. The egg-laying commences soon 
after the cocoon is begun, and the eggs are arranged 
side by side in the cocoon standing upon one end, 
being fastened in position by silken threads. A space 
above the eggs is filled with very loosely woven silk. 
In closing up the cocoon a peculiar plate-like struc- 
ture is formed of very closely woven silk, and this 
ends in an upward projection known as the “mast.” 
The purpose of this ‘‘mast’’ is not known. It is 
not a tubular structure, but merely a band of silk. 
It has been stated that if it is cut off the eggs die, 
but in the case of another species I have hatched 
eggs removed from the cocoon and submerged, so that 
the suggestion that the mast is necessary for keeping 
up the air-supply is without foundation. 
I shall not weary you with details of the develop- 
ment of the embryo beyond mentioning that, unlike 
Dytiscus, the embryo from the first occupies the whole 
length of the egg, and that the nerve chord, again 
unlike Dytiscus, grows with the embryo as it develops. 
The only other point I need mention is that in the 
cocoon all the embryos develop head downwards. 
The egg-laying period of Hydrocharis extends from 
about the middle of May until about the middle of 
Tuly in my tubs, but it may perhaps be rather longer 
in the south-eastern parts of England. The incuba- 
tion of the egg occupies nine or ten days, and, as in 
the case of Dytiscus, towards the end the embryo 
is very tightly packed within the shell. There is, 
however, no special hatching apparatus that I have 
been able to find. The pulsating organ or sucking- 
pump in the head is visible, and there are also move- 
ments of the embrvo, but at the end the skin splits_ 
along the back and the larva treads it off, giving a 
peculiar backward wriggle. . 
Now, under normal conditions the newly hatched 
larva does not at once leave the cocoon; in fact, it 
does not appear for one or even two days after hatch- 
ing. As soon as it bursts the egg-shell it wriggles 
backwards out of the egg into the space above all 
the eggs, and it is interesting to note that the hairs 
on the body of the newly hatched larva all point 
forwards. As the larve hatch, the empty shell and 
the silk bindings become broken down—I think they 
are chewed by the larve—and the whole cocoon ulti- 
mately becomes filled with the larve. 
In those cases where I dissected the eggs out of 
ee Crewe 
———— eo 
