3134 THE JOINTED ANIMALS 



all the sides of the head, and very nearly meet on its crown; and by the structure 

 of their lower lip, in which the median terminal piece is short and slightly divided 

 at the end, while the very broad palps spread out and overlap it in front. The last 

 characteristic is useful in distinguishing the Libellulidce from the next family, which 

 in many respects they resemble. Their larvae breathe by means of internal gills, 

 and have a mask which is hollowed out on the inner side, and somewhat resembles 

 a helmet. Members of this family are found in most parts of the world, and about 

 twenty species occur in Europe. The sEschnida have eyes even larger than those 

 of the Libellulida. The end piece (ligula) of their lower lip is not divided in front, 

 and not exceeded in length by the palpi; while each of the latter is armed with a 

 strong tooth or spine. The abdomen is long, narrow, and cylindrical. Their larvae 

 are more elongate, and have bigger eyes than those of the last family. The flat mask 

 has the palpi narrow, and armed with a movable hook at the tip. Like the larvae 

 of the Libellulidce they are provided with intestinal gills. Some of the largest 

 dragon flies belong to this family. 



The Agrionidcz form a family of slender-bodied dragon flies, which have both 

 pairs of wings shaped nearly alike. They are further distinguished from the other 

 two families by the shape of the head, the smaller size of the eyes, and the structure 

 of the lower lip. The head has a projection at each side, at the end of which is 

 placed one of the two hemispherical eyes; and on the wide space, lying between the 

 compound eyes, there are three ocelli arranged in a triangle. The lower lip con- 

 sists at its free end of three parts of nearly equal length; the median piece (ligula) 

 being notched in the middle, while the two palpi consist of two joints, of which the 

 first is large and terminates in an inwardly curved spine, whereas the second is 

 small and articulated with the first, outside the base of its spine. The larvae may 

 be known by the three leaf-like tracheal gills at the end of their body, which are 

 wanting or inconspicuous in those of the other families. This family contains many 

 of the most brilliantly and variously colored dragon flies; the sexes of the same spe- 

 cies often differing in coloration. Some of the exotic species attain a great length, 

 but this is brought about by the elongation of their slender abdomen without a cor- 

 responding increase in the proportions of the other parts of the body. 



The dayflies, or May flies (Ethemerida) t constituting the second 

 May Flies , i , 



group of the Pseudoneuroptera, are comprised in a single family. 



They have soft and fragile bodies, with a long ten-jointed abdomen, bearing at the 

 extremity two or three long, bristle-like, .and many-jointed tails. The hind-wings 

 are sometimes wanting, and, when present, are always much smaller than the front 

 pair, the latter being usually three sided, with the corners rounded off. Three 

 ocelli, in addition to the two large compound eyes, are borne upon the head; and 

 the antennas are short, and composed .of two stout basal joints, followed by a slen- 

 der, many-jointed bristle. In the adult the mouth organs are never well developed, 

 but remain small and soft. The jaws have no function to perform, as the perfect 

 insects do not eat, but devote entirely to other pursuits the short span of life 

 remaining to them. The common notion that the life of the May flies in the winged 

 state lasts but a single day is sometimes, but not generally, true, many being able 

 to live several days, provided the atmosphere be not too dry. There are some. 



