304 
BULLETIN OF THE BUREAU OF FISHERIES. 
Habits of the larva .- — This larva swims with a sinuous motion of the whole body up and down after 
the manner of a flatworm. There are no swimming fringes on the legs, but instead the eight posterior 
pairs of lateral gills are heavily fringed on both sides, and thus serve for locomotion as well as for breath- 
ing. By lashing them up and down the larva can move either forwards or backwards with great rapidity. 
On the land it crawls quite rapidly; being unable to lift the posterior part of the abdomen above the 
ground, it aids locomotion by using the last segment with its hooks like the posterior prolegs of the 
caterpillar, arching the abdomen upward like the so-called inchworm. It can also jump quite a dis- 
tance by snapping its body in the same manner as the Thermonectes larva. When two larvae come 
together out of the water, the first instinct is self-preservation, and each jumps back as far as it can. 
In an aquarium the larva rests nearly always on the bottom and not on the water plants, and the 
abdomen maintains a constant trembling motion up and down, which is evidently its mode of breath- 
ing. Hence, it never needs to come to the surface for an air supply. 
It is not very voracious but will defend itself fiercely when attacked and will catch anything that 
is unfortunate enough to crawl against it. It sometimes attacks and kills small fish as is related on 
page 250. It shows a preference for the nymphs of damselfleis and mayflies and the larvse of Corethra 
and Chironomus. 
Description of the larva . — The larva has the appearance of a small centipede, owing to the presence 
of lateral gills along the abdominal segments (fig. 84). When full grown it measures 25 to 30 mm. in 
length and 3 to 3.5 mm. in width. The body is made up of the head, 3 thorax and 10 abdomen 
segments, and is seven times as long as wide and strongly flattened. The general color is white, lighter 
on the ventral surface and in the lateral gills, and faintly tinged with yellowish-brown on the dorsal 
surface. The eyes are black, but the following parts are dark brown — the mandibles, a triangular spot 
between the bases of the antennae and the eyes, the neck on both the dorsal and ventral surfaces, the 
posterior margin of the dorsal plates on the first thorax segment, and a small spot on the dorsal surface 
of the base of each leg in the shape of an inverted V- 
The head is elliptical in outline, one-third longer than wide, flattened dorsoventrally, but with 
both surfaces convex, almost squarely truncated anteriorly with a small rostrum on the mid line, bordered 
on either side by a short pointed tooth. The antennae project from the dorsal surface of the head behind 
the outer corners of the bases of the mandibles. Each is four-jointed, the three terminal joints filiform 
and diminishing a little in length and diameter, the basal joint much wider and shorter. The mandibles 
are alike, each is slender, curved, acute, and suctorial, the inner tube opening through a slit near the tip. 
The maxillae are a little longer than the antennae and are attached to the ventral surface of the 
head just inside the bases of the mandibles. The basal joint is long and stout, the second joint about 
half the length but nearly as wide. To its outer corner is attached the four-jointed palp, the three 
distal joints about the same length, the proximal one about half as long. At the inner corner is a long 
curved process, emarginate at the tip, representing the lacinia, and between the lacinia and palp is a 
two-jointed galea, the terminal joint much longer and narrower than the basal, both joints armed with 
a long seta. There are also two setae on the dorsal surface opposite the base of the galea, two on the 
outer margin near the basal joint, and a small curved spine on the inner margin at the base of the lacinia. 
The labium is peculiar in that the bases of the palps are fused on the mid line; the palps themselves 
are three-jointed with a small fold or wrinkle between the first and second joints; obviously there is 
no chance for a ligula. 
As in the Dytiscidae, the eyes are 12 in number, a group of 6 just behind the base of each antenna 
and all visible in dorsal view. Their arrangement may be seen in figure 85, p. 303; the two dorsal eyes 
are close together with their long axes at right angles to each other. The other eyes are separated a 
short distance laterally and a much longer distance longitudinally, and their long axes are parallel, 
respectively, to those of the dorsal pair. All the eyes protude slightly from the surface, and in the 
space between them a seta is located. Posteriorly the head is narrowed into a short neck, covered with 
two narrow plates on the dorsal surface, but naked on the ventral surface. 
The three thorax segments are about the same length, but the first one is a quarter narrower than 
the other two and carries a pair of dorsal plates. The other segments and the abdomen are destitute 
of dorsal plates, since this is not a burrowing larva. 
The 10 abdominal segments are represented in length by the numbers 11, 15, 18, 18, 19, 19, 20, 20, 
15, 10, and in width by the numbers 28, 31, 33, 35, 34, 34, 33, 30, 21, 8. From the posterior corners of 
