Objects for the Microscope. 85 



There are, however, other and quite different modes of 

 respiration in aquatic larvae, which form beautiful micro- 

 scopic objects. 



AERATING LEAFLET OF LIBELLULA, 



the larva of one of the Dragon-flies, those slender, beau- 

 tiful blue and scarlet flies, which glance like living sun- 

 beams across our path on a summer's day, and may be 

 found in thousands resting on the reeds and bushes at the 

 river's side. When these are in the larval state, they have 

 three leaflike plates at the extremity of the abdomen, over 

 which innumerable tracheae ramify and draw from the 

 water that supply of air which is needful for their life. 



ABDOMEN OF EPHEMERA, OR SPIRACLES. 



The larva of the pretty May-fly, or Ephemera, has on 

 either side of its body a row of little leaflets, each of which 

 is an external spiracle, and when alive it is most interesting 

 to watch its palpitations, the play of those tiny organs 

 drawing oxygen from the water to aerate the blood. It is 

 best thus to see it, because we are able to observe the 

 circulation of the blood through the transparent skin. 



CIRCULATION OF BLOOD. 



All creatures that have life have blood : it is the nourish- 

 ing fluid which is needful for existence. In insects, it is 

 colourless, but composed of minute corpuscles, which are 

 propelled through the body, not by arteries and veins, but 

 by one great dorsal vessel, constricted at intervals, and one 

 end of which is closed, the other open and acting as the 

 aorta of the heart. We see it here constricting and dilating, 

 pumping out the blood which bathes the whole interior of 

 the body, flowing into the antennae, the legs, the wings- 

 taking all directions. Here also we see a regular current 

 through each appendage of the tail, and backward it is drawn 

 into the long dorsal vessel through some lateral fissures in 

 it, which are closed by valves, preventing its return. More- 

 over, we can see in this larva the constrictions of the heart, 



