Hi 



EVENINGS AT THE MICKOSCOPE. 



geographical simile, we niav say that, instead of being 

 an island in the midst of a lake, it is a promontorj. 



Tims, the breathinoj space is a 

 crescent-shaped band, wliich is 

 crossed in every part by bars 

 passing from the margin to the 

 projecting plate. But, as if the 

 interstices left by these bars 

 wonld be too coarse for the pur- 

 pose, they are further sublimat- 

 ed by a membrane, ■which is 

 stretched across them, and 

 which is perforated M-ith a num- 

 ber of excessively minute round 

 lioles, througli which alone the air is admitted. 



In many of the two-winged flies, which inhabit the 

 water in their earlier stages, there are some interesting 



contrivances and modifica- 

 tions connected with the or- 

 gans of respiration. It is ne- 

 cessarv that the orifices of 

 the air-tubes should be 

 brouo-ht at inters'als to the 



6PIEACLE OF LEATIIEU-COAT. 



surface of the water, in or- 

 der to come into contact 

 with the external air ; while, 

 at the same time, it is im- 

 j^ortant that as small a por- 

 tion as possible of the ani- 

 mal's body be exposed to 



danger, by being protruded from its sheltering element. 



An example in point you may see in this vase. 



Here is a slender worm, an inch and a half in 



SPlr.ACLE OF COCKCIIAFEE-GKCB. 



