SAW FISH SAW FLY 653 has the elongated and rounded form of a shark, with the mouth and gill openings on the ven- tral surface as in rays. Its distinguishing char- acter is the long, flattened, narrow, and straight snout, set on the sides with teeth or strong bony spines, forming a double-edged saw-like weapon, whence the common name. The true jaw teeth are very small, and pavement-like as in the rays ; the body is flattened in front of the pectorals, the posterior portion and the tail as in sharks ; the skin is covered with small rough scales; the pectorals are distant from the head, and not extending to the ventrals; the tail has two dorsals, and a caudal fin pro- longed as in the sharks. About half a dozen species are described, found in arctic, tropical, and antarctic seas, and one all along the coast from New England to Florida; they are rapid swimmers. The beak attains a length of from one fourth to one third the total length of the body ; it is covered with a rough skin, and is narrower toward the end, which is rounded; this beak has been found driven deeply into the timbers of ships. They seem to have a natural antipathy to the larger cetaceans, and many voyagers have been witnesses to their victories over them. The jaw teeth are adapt- ed for crushing crustaceans and similar ani- mals upon which they feed, and not for tear- ing flesh. According to Owen, the beak is composed of the cartilages attached to the frontal, nasal, and vomerine bones blended into a horizontal flattened plate, which is more completely ossified than any other part of the skeleton ; a series of deep sockets on each of the lateral margins contain the teeth, which are solid, the base being slightly concave and porous, and the spaces between them hollow and filled with a gelatinous medulla, rendering it light without diminishing its strength ; ves- sels and nerves supply the teeth, which grow by constant Addition of ossified pulp material at the base. Though the projections of the beak are implanted like teeth, they have no relation to the intestinal canal, and are turned outward like spines of the external or der- matoskeleton ; they form a very interesting transition between teeth and cutaneous spines. These teeth wound by repeated blows, and not by cutting like a saw ; the Polynesians use this beak as a sword. The common saw fish is the P. antiquorum (Lath.), which attains a length of 12 to 15 ft., of which the beak is about one third, with 20 to 30 teeth on each side ; it is Common Saw Fish (Pristis antiquorum). blackish gray above, and lighter below; the eyes are large, the nostrils in front of the mouth protected by a membranous fold, and two oval foramina behind the eyes. Klein says that in the embryo the sides of the snout are as smooth as the gums of a new-born in- fant ; but according to Latham they grow very rapidly after birth, and are not shed and re- placed like the teeth of mammalian jaws. SAW FLY, the popular name of the tenthre- dinidce, a very destructive family of hymenop- terous insects. They are found on the leaves of plants, and live almost entirely on vegeta- ble food; they are poor fliers and sluggish; the form is generally short and flattened, with broad head, and thorax widely joined to the abdomen, the antenna short but of various forms, thread-like, knobbed at the end, feath- ered, notched, or forked ; the wings overlap, cover the back, and are horizontal when closed. The females have two saws, lodged in a groove in the hind part of the body within two sheath- like pieces ; they are placed side by side, with the ends directed backward, the form and the shape of the teeth varying; they usually curve upward, and are serrated along the lower or convex edges ; each saw has a back to steady it, but the blade slides forward and backward on it ; they are not only toothed on the edge Elm Saw Fly (Chubex ulmi). but on the sides, acting as rasps as well as saws. With these they saw slits in stems, leaves, and fruits, in which their eggs are de- posited ; the wounds sometimes produce galls in which the young are hatched and grow. The larvae look much like caterpillars, are cy- lindrical and greenish, with several pairs of legs, generally 18 to 22 ; most are naked, but some have a few prickles, others a white flaky substance, and a few a dark, slimy, slug-like skin. The larvae also resemble caterpillars in habits ; when fully grown they enter the ground and make a silken cocoon, but a few place their cocoons on plants or in crevices above ground ; they remain thus during the winter, change to whitish chrysalids in spring, and soon come out winged insects ; there are some- times two broods, one going through all ita changes during summer. About 100 species are found in New England alone. The largest is the elm saw fly (cimbex ulmi, Peck), about |- in. long, with an expanse of wings of near- ly 2 in. ; the female resembles a hornet, with black head and thorax, hind body steel-blue with three or four yellowish spots on each
