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BULLETIN OF THE BUREAU OF FISHERIES. 



sized cupules on long stalks. The basal segment has two rows, one of 15 cupules across the center of the 

 segment and another of 20 cupules along the distal margin. The proximal half of the basal joint is 

 covered with fine hairs. The second segment has a single row of 21 cupules, and the third segment a 

 single row of 20 cupules, both along the distal margins. There is also a band of short hairs on the ventral 

 surface of the basal joint of the tarsus of the second legs and three or four coarse folds at the apex of the 

 hind coxae. 



Wickham has given a short description (1893, p. 324) of the male tarsus of this species with a figure 

 (pi. 5, fig. 2). He also described and figured the male tarsus of Cybister explanatus from California (pi. 

 6, fig. 4), and described without a figure that of Cybister tripunctatus, an African species. The obsolete 

 claw of the hind tarsus of the female varies much in size. In one specimen it could scarcely be detected; 

 in another it was nearly a third as long as the large claw. 



In all the other beetles raised from larvae the adult emerged perfectly formed, except in one 

 instance. Of the Cybister adults, however, 75 per cent were malformed in some particular. A front leg 

 was lacking in one, a hind leg in another, some of the mouth parts in a third, a fourth had a wry 

 neck, and so on. Whether this is true also of those that emerge under natural conditions could not be 

 determined. 



Genus DYTISCUS Linnaeus. 



Dytiscus (Linnaeus, 1758, p. 411). 



This is another genus of large beetle, of which both the larvae and the adults 

 kill and eat young fish. These beetles are dark, olive-brown in color, with a dull 

 yellow stripe along the sides of the thorax and elytra; the front and hind margins 

 of the thorax are also usually yellow. The claws are equal in both sexes, and in 

 the males the basal joints of the front tarsi are broadly dilated and armed with 

 sucking disks of different sizes. 

 Dytiscus verticalis Say. Figures 34-38. 

 Dytiscus verticalis (Say, 1825, p. 92). 



Eggs. — No direct observations have been made with reference to the eggs of this species, but they 

 are probably deposited singly in incisions made by the female with her ovipositor in the stems of water 

 plants in a manner similar to that followed by the female of Dytiscus marginalis. 



Habits of the larva. — The material for this species consists of three adults, one of which was taken 

 from a pupal chamber, a larval skin from the same chamber, and two larvae nearly full-grown. This 

 larva, like that of Cybister, swims more by means of the fringe along the lateral margins of the last two 

 abdominal segments than by its legs. The latter are poorly fringed with swimming setae, but make 

 up for it in their length. When swimming slowly, the legs are used alone, but in rapid locomotion the 

 whole body contributes. This larva also can jump to a considerable distance by sudden flexure of the 

 last two abdominal segments, and it can do this on land as well as in the water. According to Brocher 

 (1913, p. 125) when the Dytiscus larva breathes it may either stand upon some sort of vegetation and 

 reach upward, thrusting the tip of its abdomen above the surface of the water, or, releasing its hold on 

 the vegetation, it may float slowly upward, the abdomen preceding, until the tip of the latter reaches 

 the surface; or, when the specific gravity of the body is greater than that of water, it may swim with its 

 head directed upward and on reaching the surface turn parallel to the latter and thrust its abdomen 

 above the surface. In all three cases the cerci are turned down against the surface film, this action both 

 opening the posterior spiracles and supporting the larva while it breathes. 



With reference to food we find the following statements, which were made not of this particular 

 species but of the genus in general. Evermann and Clark (1920, Vol. I, p. 639) stated that the larvae 

 of Dytiscus attack the tadpoles of the leopard frog and devour them. Dytiscus larvae were found by 

 Needham and Williamson (1907, p. 485) in the " Gym" pond on the campus at Lake Forest, 111., feeding 

 upon Corethra pupae. Wright (1920, p. 42) stated: "The water beetles, especially their larvae (water 

 tigers) and dragonfly nymphs also take their heavy toll of tadpole lives." Miall (1895, p. 47) made 

 the statement: "Alntost all kinds of aquatic animals, snails, worms, insects, tadpoles, and fishes are 

 devoured by the insatiable Dytiscus larvae." Garman (1890, p. 163) testified: "Both adults and young 

 lead a predatory life, attacking and devouring whatever they can master. They do not hesitate to attack 

 animals many times larger than themselves and are very destructive in fishponds to young fishes. They 

 are in turn eaten by the larger fishes." 



