OF THE GNAT AND BUG. 103 



are disturbed, and then they sink, or make to the bottom directly ; and, 

 as soon as the agitation in the water has ceased, they directly make 

 their way again to the surface. When they move down they go with 

 their heads foremost ; and they ascend without changing the same 

 position, moving with the tail uppermost or going backward. Their 

 progress is by the alternate zigzag motion of their body. When not 

 disturbed they hang by their tails on the surface of the water ; and, 

 when there are many of them, they make a pretty object. The end of 

 the tail, which stands out from the end of the body, making with it an 

 obtuse angle, has, I suspect, either some oil in it, or it can throw out a 

 hollow cone, which, being filled with air, suspends the body ; for, when 

 the end of the tail comes to the surface, the water is repelled, not 

 allowed to touch the very end. When not suspended by the tail, nor 

 moving with their bodies, they slowly sink, and therefore are specifically 

 heavier than water. 



To ascertain whether they breathed air, I filled up the glass in 

 which they were with water full to the brim, and then covered it with 

 a piece of flat glass so that the surface of the water touched the under 

 surface of the glass, by which means no air was opposed to the surface 

 of the water : they immediately came to the top, but they could not be 

 suspended, and in those attempts they soon died, being drowned for 

 the want of air. When suspended in the water, there are some parts 

 about the mouth or head constantly in motion. 



The gnat can hardly be said to go into the chrysalis state, as in 

 many other insects : it does not leave the water, nor does it enclose 

 itself in a coat spun out of itself, but seems to be more motionless or 

 less frisky, more coiled up upon itself, forming a round body with a 

 globule of air on the back, which makes it swim. Its head-part seems 

 to become larger and of a darker colour, and the belly, or what is 

 commonly called tail, becomes rather less ; yet in this state it has 

 motion when disturbed, and sinks by its motion. I imagine that in 

 this state new parts only are forming under the skin, not a change 

 going on, and that, when completely formed, they emerge out of the 

 old skin, leaving it swimming in the water, as it were hanging by the 

 tail. 



The Aphis Abietis also does not go into the chrysalis state. 



Of Bugs \_Cimex lectularius\. 



Query. How do bugs live ? what do they eat ? 



They suck blood and fill themselves full. It is supposed there are 

 some people that they do not bite, and others they do ; but most pro- 



