414 NATURAL HISTORY OF ARTHROPODS. 



The head is fully differentiated, and usually has eyes ; the jaws are thickly ciliated, 

 or fringed with hairs, by the means of which a current of water is produced that brings 

 little particles of food within the reach of the mouth. 



After changing their skin two or three times they assume a more club-shaped 

 appearance, in which the parts of the adult insect are indistinctly seen. The abdomen 

 terminates in two leaf-like appendages that act as propellers; but in general these 

 pupa? remain near the surface, except when disturbed, and take no food. The 

 breathing organs are no longer a tube at the tip, but there are now two that spring 

 from the sides of the thoracic segments. Finally, when the perfect mosquito is ready 

 to emerge from the pupa, the back of the skin, which has now come to the surface and 

 is exposed, splits, and the fly carefully and gradually extricates itself from the mem- 

 brane which thus serves the place of a raft till the future legs and wings are sufficiently 

 firm. But right now is the period of the mosquito's life most fraught with danger ; a 

 wavelet, a breath of air, or a raindrop hopelessly shipwrecks the frail bark. This is 

 why running waters are free from these insects. 



Hitherto only aquatic larva? are known in this family, yet it seems probable that 

 some species must undergo their transformations in the earth. On the high, dry 

 plains east of the Rocky Mountains they are, during many years, extremely abundant, 

 often many miles from the nearest water or moist ground, and in a region where 

 standing water is almost unknown. 



The adult insect is found nearly everywhere, in some places in almost incredible 

 numbers, forming swarms in visible clouds. Instances are recorded in some localities 

 not only of loss of life among cattle and horses, but also of human beings, from their 

 bites. One can understand why there should be so many, for there are several broods 

 during a season, the female laying in all about three hundred eggs. Were all' the 

 conditions perfect a single female might produce, at the end of four months, many 

 millions of progeny. When the weather is no longer favorable, the female retires to 

 some sheltered spot and remains during the winter, but even in New England these 

 insects may be seen every month in the year. 



The family TIPULID^B comprises the largest of the flies with long antenna?, some of 

 them more than two inches in length. The legs are very elongate, and very delicate, so 

 delicate indeed that one seldom succeeds in capturing them without the loss of one 

 or more. They will at once be distinguished from all the allied families by the pres- 

 ence of a complete V-shaped suture on the dorsum 

 of the thorax ; at the same time the wings will be 

 found to contain numerous veins and a perfect 

 discal cell. These alone will suffice to recognize 



FIG. smpiasma fitchii. s P ecies belonging here. The female differs, more- 

 over, from all other nematocerous flies, in having 

 nearly always the ovipositor composed of two pairs of long, horny, pointed valves ; 

 these are for the purpose, so rare among Diptera, of depositing the eggs within 

 the ground, or other firm substances. This they do by standing nearly upright, 

 and thrusting the ovipositor downward leave one or two eggs, then, moving a 

 little forward, this operation is repeated till all are laid. When the weather is 

 favorable the eggs hatch out in little more than a week. The larva? are ash- 

 gray in color, usually more or less transparent, of twelve segments ; the head is 

 incompletely differentiated and retractile, and has the maxilla? and mandibles more 

 or less horny and stout; there are short, fleshy antennae. The organs of locomo- 



