310 



BULLETIN OF THE BUREAU OF FISHERIES. 



The newly hatched larva. — The newly hatched larva is 2 mm. long and 0.35 mm. wide through the 

 metathorax. It is light gray in color, the chitin areas tinged with yellowish-brown, and the entire 

 surface covered with minute setae. The legs and lateral gills are much longer in proportion to the body 

 than those of the mature larva, and the metathorax is wider than the abdomen, but otherwise it is an 

 almost exact minature of the mature larva. 



Habits of the larva. — These larvae are very sluggish; they can not swim at all but crawl about slowly 

 over the vegetation, their long tracheal gills standing out rigidly on either side like rods. They cover 

 themselves with green algae and lie inert for hours at a time, only coming out after food. When dis- 

 turbed, they curl up slightly and feign death, and it is often difl&cult to determine whether they are 

 really dead or not. They are the most inactive of all the larvae here studied but are as persistent crawlers 

 as the Peltodytes larvae. They can not be kept in a mud cell unless the latter is securely sealed. 

 They are also hard to kill and will live for an hour or an hour and a half when placed in 95 per cent 

 alcohol. They breathe entirely through the lateral gills, which contain tracheoles, and hence have 

 no need to come to the surface for air. They eat, as far as could be observed, nothing but algae, Chara, 

 Nitella, etc. Two larvae were kept a long time in an aquarium with an abundance of Entomostraca, 

 snails, and insect larvae of various kinds. They refused them all and ate only vegetable food. 



Description of the larva. — General form spindle-shaped, slightly depressed, widest through the 

 second abdominal segment, much narrowed both anteriorly and posteriorly. Total length on the mid 

 line 10 mm.; greatest width 2.5 mm.; greatest thickness 2 mm.; length of posterior gills 3 mm. Body 

 made up of the head, 3 thorax segments, and 8 abdomen segments. Each of the first seven abdomen 

 segments carries a single pair of tracheal gills, which are cylindrical and threadlike and increase in length 

 from in front backwards. These gills, unlike those of the gyrinid larva, are entirely naked. The last 

 segment has no gills and is very small. Color a grayish-yellow, deepening to brown on the thorax 

 and along the sutures between the joints. 



Head quadrangular in outline ; antennae three-jointed, joints diminishing greatly in length and width; 

 first joint with a sensory papilla on the inner margin at the distal end; second joint with a long seta at 

 the distal end on the inner margin and a sensory papilla on the outer margin; third joint minute, armed 

 with three unequal setae. 



Mandibles asymmetrical, the right one with three blunt conical teeth on the inner margin, the 

 distal tooth the largest, the middle one less than half as large, and the proximal one a mere knob. The 

 left mandible also has three teeth, nearer the base, much closer together and about the same size. Just 

 above them and hiding them in dorsal view is a bunch of radiating comblike spines. 



The maxilla is five-jointed, the basal joint more than twice the combined length of the other 

 four, with a large seta on its inner margin. The second joint is short and subquadrate and bears on its 

 inner margin a small knob armed with a sensory papilla and a seta. Of the remaining joints the fourth 

 is longer than the third and fifth combined, while the fifth is tipped with four small sensory papillae. 

 The labial palps are two- jointed, the distal joint twice the length of the basal and tipped with a single 

 seta; there is no ligula. 



The eyes are behind the center of the head and are arranged as shown in Figure 103 (opp . p. 309) . The 

 first six abdominal segments are each divided into a larger anterior portion bearing the lateral gills and 

 a smaller posterior portion; the last two segments are entire. Each anterior portion is further divided 

 by a transverse groove or wrinkle. 



Pupation. — The larva crawls but a short distance from the water's edge and hollows out its pupal 

 chamber in the soft earth 1^ to 2 inches beneath the surface. It occasionally pupates within 24 hours 

 after the completion of the chamber but more often remains several days before transforming. 



Muttkowski (1918, p. 414) stated with reference to the family Hydrophilidae: 



Only a single species, Berosus sp. (probably striatus) Say, is represented in the lake (Mendota), and this species is 

 quite rare. The larva occurs in sandy depths up to 6 meters. I was able to breed the species and discovered that the pupa 

 is aquatic and a water-breather like the larva, but the emerged adult escaped before 1 had seen it. 



If he had seen the emerged adult he would have discovered his mistake, for this pupa is certainly 

 terrestial like all the others here described. 



Description of the pupa. — General form an elongate oval, 6 mm. long and 3.25 mm. wide, the pos- 

 terior end rather bluntly pointed. The color is white, usually with a decided greenish tinge; the eyes 

 are at first light brown but deepen with age. Just before emergence the white changes to yellow, the 



