INSECTA. 



water, in which her offspring are destined to pass the earlier pe- 

 riods of their existence, gluing the ova together at the moment of 

 their extrusion, so as to unite them into a boat-like mass (Jig. 

 133, A) of such beautiful construction that the little bark swims 

 secure from injury, even during the roughest weather. The in- 

 dividual eggs are of a conical form (fig. 133, B, a, 6, c), and are 

 closed at their inferior extremity by a kind of lid (rf), provided 

 to give egress to the mature embryo. The larva (c), represented 

 upon a magnified scale at E, bears not the slightest resemblance 

 to the perfect insect, and is provided with a singular modification 

 of the respiratory apparatus adapted to its habits. The head is 

 large, and carries two ciliated organs (g, g), which by their 

 movements bring food towards the mouth ; the thorax is even 

 larger than the head, and is furnished with fin-like bunches of 

 minute hairs, as likewise are the segments of the abdomen. To 

 the extremity of the tail is appended a group of moveable leaflets 

 or fins, so disposed that by their action they sustain the larva at 

 the top of the water, where it generally remains suspended with 

 its head downwards. Such a position would obviously render 

 respiration impossible, was there not a corresponding arrangement 

 of the breathing organs to allow of free communication with the 

 air. For this purpose, the respiratory trachese are found to be 

 connected with a tube appended to the antepenultimate segment 

 of the abdomen, the perforated extremity of which, being raised 

 above the water, procures from the atmosphere the oxygen re- 

 quired for respiration. After several moults, the larva, having 

 attained its full growth, enters the pupa state, and in this con- 

 dition still remains an inhabitant of the water, and occupies a 

 position near the surface. A remarkable change, however, is visible 

 in all parts of its structure : the head and thorax (Jig. 133, D) 

 are consolidated into one large mass, under which the lineaments 

 of the mature insect may be detected ; while the tail still con- 

 tinues to be the agent employed in natation. The condition of 

 the respiratory organs is, moreover, completely altered : the tube 

 fixed upon the antepenultimate segment of the larva has totally 

 disappeared, and, instead of it, we find two tubes appended to the 

 back of the thorax ; these, although they perform the same office 

 as the anal pipe of the larva, are thus displaced, in order to cor- 

 respond with the altered position in which the animal now swims ; 

 the back of the thorax, and not the tail, being nearest to the 

 surface, as represented in the drawing (D). The necessity for 



