HYMENOPTERA. 143 



thin delicate vessel, dilated opposite the thorax, and 

 beating or contracting at regular intervals. This is 

 the dorsal vessel, the dilatation representing the heart 

 of the higher animals ; and it serves to propel the 

 colourless blood throughout the body. 



After several moultings or castings of the skin, to 

 allow of the growth of the insect (for insects grow 

 only in the larval state), the larva becomes trans- 

 formed into the pupa (PL X. fig. 8). In this state 

 the animals still move about in the water, and are 

 often found suspended from its surface by two respi- 

 ratory tubes, which, however, are not connected with 

 the tail, but arise from the thorax; and the various 

 parts of the perfect insect may be seen through the 

 case or skin, within which they are closely packed. 



When the pupa has attained its full development, 

 the perfect insect emerges from it, leaving the water 

 to fly about and seek food. 



TIPU'LIDJE. In the water of ponds and pools a young 

 larva (PL X. fig. 31) will often be met with, which 

 is that of Chiron omus plumostts, a largish gnat- like 

 insect, belonging to the daddy-long-legs family (Tipu- 

 lidse). This larva exhibits the usual thirteen seg- 

 ments, including the head. In the young state the 

 body is nearly colourless ; but in the mature larva it 

 is of a blood-colour, and about an inch in length. 

 Beneath the first joint of the body are two foot-like 

 processes covered with hair; and at the end of the 

 body are also two processes, surmounted with hooks. 

 The three last joints of the body are also furnished 

 each with a pair of fleshy processes, those of the first 

 pair being very short. 



HYMENOP'TERA (v/j,r)v, membrane, irrepov, wing) . 

 This, which forms the sixth Order of insects, contains 

 the bee, the wasp, the ant, &c. 



In the Hymenoptera there is a curious contrivance 

 for linking the two wings on each side, so that they 

 may form a single piece in the flight of the insect. 



