WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
325 
portion, and along each lateral margin is a fold of skin that is raised into a papilla near the center of the 
posterior portion of each segment. There are similar folds on the dorsal and ventral surfaces close to the 
lateral fold, and they also are raised into papillae opposite the lateral papillae. Between the dorsal and 
lateral papillae and a little in front of them lie the spiracles, which remain closed until the time of pupa- 
tion. 
The color is yellow, tending to orange on the head and thorax, lighter and grayish on the abdomen. 
The eyes are black, and the following markings are cinnamon brown: The tips and teeth of the mandibles; 
a stripe through the center of the head lengthwise, containing a herringbone figure of deeper brown; 
a spotted area on either side behind the eyes; four longitudinal stripes on the ventral surface of the head; 
irregular markings on the dorsal surface of the thorax and abdomen, as shown in Figure 129 (p. 323). 
The ventral surface of the thorax and abdomen is dull yellow. In general, the brown markings increase 
with age, and when the larva enters the pupal chamber the entire dorsal surface is dark brown, almost 
black. 
The antennnae are even more slender than in the newly hatched larva; the basal joint is more curved 
and becomes sparsely fringed with long hairs on its inner margin. The base of each antenna is about 
half-way between the lateral margin and the mid line. The mandibles also remain slender, but become 
blunter with age; the proximal tooth on the inner margin of the left mandible becomes smaller and often 
entirely disappears. The maxillae are practically unchanged, except that the palpifer has increased 
slightly in relative length. The labium now has a transverse row of large spines across its dorsal surface 
near the base; the palps are two-jointed, the terminal joint four times as long as the basal and tipped 
with one long seta and several short ones. 
Each of the longitudinal tracheae is enlarged in the last two abdominal segments and acts as a reservoir 
for air. The two open into the bottom of a transverse pocket just beneath the dorsal surface at the pos- 
terior margin of the last segment. The overhanging dorsal surface is rounded into four narrow lobes and 
forms the roof of the pocket or atrium. The floor is formed by the ventral surface, which is divided 
into three lobes, the median one much longer and wider than the lateral ones, and all projecting con- 
siderably beyond the dorsal surface. Each lateral lobe carries on its posterior margin a claw that curves 
upward and assists in keeping the atrium closed while the larva is beneath the water. On the floor in 
front of the opening of each trachea is a large finger process, projecting upward and tipped with long 
hairs. Nearer the median line and farther back is another pair of much smaller processes, also projecting 
upward and tipped with a single long hair. The breathing apparatus thus resembles very closely that 
described by Miall (1895, p. 91) for Bydrobius fuscipes. 
Pupation . — When fully grown, the larva crawls quite a distance from the water’s edge and hollows 
out a pupal chamber from 2 to 2J inches beneath the surface, in which it remains two or three days 
before pupating. It continues to breathe through the atrium, and the spiracles do not function until 
after its transformation. 
Description of the pupa . — General outline elongate-obovate; greatest width 4 mm. through the bases 
of the wings; total length, including the cerci, 9 mm. Color at first a pale greenish-white, becoming 
snow-white in preservatives, except the eyes, which are reddish-brown. On the dorsal surface the 
styli are arranged as follows: 10 along the anterior margin of the pronotum longer than the others; 4 
smaller ones near the mid line and removed a little from the margin; 2 posterior to the center of the seg- 
ment; 1 on each lateral margin and 8 across the posterior margin; 1 either side of the scutellum on the 
mesonotum; 2 on the metanotum; 4 on the first abdominal segment; 6 on each of the following six seg- 
ments, the two lateral ones close together and mounted on small tubercles; 2 much smaller ones on the 
posterior margin of the eighth segment at the tips of small and indistinct lobes. Each of these styli 
have a thickened, fleshy, and moniliform base, tipped with a corkscrew seta. There are no supraorbital 
styli. The ninth segment terminates in two fleshy and superficially annulate cerci, which are stout 
and divergent at the base and then curve like parenthesis marks. Each is bifid at the tip, the two points 
ending in stout spines, and there is another stout spine on the outer margin near the center. 
The antennae extend outward at right angles to the body axis; the maxillary palps reach back 
to the bases of the third legs, and the labial palps do not quite reach the posterior ma rgin of the second 
legs. The femora of all the legs stand at right angles to the body axis; the tibiae of the first legs are 
folded tightly against the femora; the tarsi are turned backward parallel with the body axis and widely 
separated. The tibiae and tarsi of the second and third legs are in line with each other, and their tips 
48790°— 23— 7 
