234 
BULLETIN OF THE BUREAU OF FISHERIES. 
attached, and the species can be recognized as easily from these discarded skins 
as from the living larvae. 
Then a search for as many pupae as could be found was made along the shores 
of the ponds, and in every instance care was taken to secure the old larval s ki n 
from the inside of the pupal chamber. In this way the larvae and pupae were defi- 
nitely related, one to the other, and the pupae were then kept in suitable terraria 
until the adult beetle emerged. On transforming from the pupa to the adult the 
old pupa skin is thrown off and may be obtained from the pupal chamber and used 
to identify the species. 
One of the best methods with the larger species, when a pupal chamber is 
found on a pond shore, is to leave it as nearly intact as possible. By cutting 
around it with a knife blade a small cube of earth containing the chamber may be 
removed. This cube can then be kept in a terrarium until the adult beetle emerges, 
and the chamber will contain both the larval and pupal skins. If the chamber has 
been opened during the removal, it should be covered again with a pellet of mud 
before being placed in the terrarium. Darkness is necessary for the best success 
in rearing the specimens. In the case of the smaller species, and often with the 
larger ones, the natural pupal chamber is destroyed when the pupa is found. In 
such cases they will thrive equally well in an artificial chamber, made as nearly 
the size and shape of the original as possible, and with a removable cover, so that 
the development of the pupa may be watched from day to day. Frequently the 
pupal chamber will be found to contain a larva not yet transformed, and some- 
times a larva can be obtained that has come out of the water but has not yet begun 
to build its pupal chamber. These can be dealt with in the same manner as the 
pupae, and if placed in artifical chambers will go on with their transformation. 
A convenient terrarium can be made as follows: Punch the bottom of a small 
cylindrical tin box full of holes and stand it upright in the center of a large iron 
pan. Fill the pan half full of sand around the upright box, then pour water into the 
latter until the sand is thoroughly wet. The cubes of earth containing natural 
pupal chambers and the artifical ones made in imitation of them can be placed 
upon the wet sand, which will keep them from drying up. By renewing the water 
in the central box as fast as it disappears the sand, and with it the pupal chambers, 
may be kept at just the right degree of moisture, which should be the same as that 
of the earth from which the larva or pupa was originally obtained. 
Certain habits of the larvae and adults, such as swimming and breathing, can 
be watched better in an aquarium in the laboratory than in their natural environ- 
ment. There are other habits, however, such as feeding, deposition of the eggs, 
and formation of the pupal chamber, upon which reliable information can be 
obtained only by watching the beetles in their normal habitat. When transferred 
to aquaria both adults and larvae will eat almost anything that is furnished to 
them. Carnivorous species usually devour animal food and herbivorous species 
vegetable food. If kept in confinement, however, under stress of hunger they may 
radically change their diet. It is probable that they are rarely compelled to do 
this under natural conditions. What they eat in an aquarium, therefore, is an 
excellent criterion of their ability to adapt themselves to circumstances and shows 
