WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
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each segment is given off a pair of narrow, conical gills, 10 times as long as wide, contracted at the base 
and tapered to an acuminate point. The ninth segment carries two on either side instead of one, and 
the tenth segment has none. Each gill contains a narrow central tracheole, and the eight posterior 
pairs are heavily fringed with hairs, although the first two pairs are naked. The tenth segment is naked, 
a little longer than wide, and armed at its posterior end with four sickle-shaped hooks, the inner one 
on either side considerably larger than the outer one. Miall (1895, p. 36) said of these hooks in the 
Gyrinus larva that they “are believed to be of use in climbing. ” They are also used during the con- 
struction of the pupa case, holding the posterior end of the larva securely in place while it gathers the 
materials for making the case. 
Pupation .— When the larva is full grown, it crawls out of the water and up the bank, and its lateral 
gills shrivel up and fall off, except the last double pair and the single pair just in front of them, which 
are used for locomotion. The distance traveled and the place finally selected appear to depend upon 
the moisture of the earth, which must be soft enough to be easily worked but not moist enough to be 
muddy. The larva is quite particular in its choice and often covers a considerable area before finding 
a location that suits it. 
Then there must be a convenient support to which the pupa case may be attached. The under 
surface of a dead grass or rush stem was usually chosen, since it was near enough to the ground for the 
larva to reach after building material and at the same time far enough removed to give the space requisite 
for the completed case. The case is made of pellets of earth stuck together with saliva. The earth 
apparently is not chewed and thoroughly mixed with the saliva after the manner of the mud wasps; 
rather, a mouthful of material is seized by the mandibles, wet with saliva, and pressed into place, and 
there is no smoothing of the outside surface or shaping by the mandibles. The outside of the case is 
rough, but the curve of the walls is quite regular. Sand grains, small fragments of rock, bits of wood, 
and pieces of leaves are mixed with the mud pellets in the walls. The larva clings to the grass stem with 
its posterior hooks and constructs the case around its own body. When the case is finished, except a 
small orifice at one end, the larva transfers enough material to the inside of the case and completes it 
from there. The case is 13 to 16 mm. long, 8 to 10 mm. wide, and is usually a fairly regular ellipsoid. 
The walls are about 1 mm. in thickness, except at the ends, where it is increased to 2 mm. A full- 
grown larva is about 30 mm. long, and hence its body must be folded inside the case ; it assumes the form 
of the letter C, the ventral surface inside. After resting two or three days the skin splits open along the 
dorsal mid line from the base of the head to the ninth abdomen segment and flattens out against the 
inside of the case. 
Description of the pupa . — General shape oblong, rather squarely rounded anteriorly, more pointed 
posteriorly, the head folded down upon the thorax and invisible in dorsal view. Length 10.5 mm., 
width 4.5 mm. through knees of first legs. Color yellowish-white, turning later into brown on the dorsal 
surface; eyes black. The eyes are divided as in the adult, each half a hemisphere, the fiat surfaces 
facing each other and connected by a narrow cord. The front of the head reaches well beyond the 
bases of the first and second legs, and the maxillary palps project diagonally from beneath the upper 
lip. The basal joints of the legs are at right angles to the body axis and the knees project beyond the 
lateral margins. The tips of the first legs meet on the mid line, those of the second legs are separated a 
short distance, and those of the third legs are widely separated. The elytra are considerably shorter 
than the wings and are squarely truncated at their tips, whereas the wings are bluntly pointed. 
On the ventral surface of the pupa there are no setae, except a ragged fringe across the anterior margin 
of the prothorax and at the posterior end of the abdomen. The dorsal surface is plentifully supplied with 
setae, as shown in Figure 93. When the pupa case is horizontal, the pupa rests usually upon its back, 
and when the case is vertical upon the tip of the abdomen. 
These pupae can not be preserved like the others in 95 per cent alcohol, nor in a mixture of 95 per cent 
alcohol and 10 per cent formaldehyde. In either preservative the pupa flattens out completely in a day 
or two and is absolutely worthless. Carnoy’s mixture of glacial acetic acid, absolute alcohol, and chloro- 
form is the only preservative tried that gave satisfactory results. 
Wickham (1893a) noted that this pupa is much more quiescent than is usual with the Coleoptera, 
and he could only detect the faintest movement of the abdomen in the specimens he observed. If the 
pupa be overturned in its case, however, or be irritated with a needle, it will prove to be lively enough 
and will wriggle about vigorously. 
