THE WATER DEVIL. 



here covered with hairs, and in the specimen from which the 

 drawing has been made, a vast number of minute bell-shaped 

 animalcules were attached to them, which will be recognised in 

 the figure. 



The abdomen is united to the chest or thorax a little above the 

 first pair of swimmers, and extends to the commencement of the 

 bifurcated tail ; along the sides of the abdomen are extended the 

 two tracheae or air-vessels, which as already explained perform 

 the functions of lungs ; they are in this case of a light blue 

 colour, and throw out numerous branches at various intervals in 

 their course. These trachea) consist of curiously formed fibres, 

 winding round them like the twisted filaments of a rope, as may 

 be seen in the figure. These vessels are usually distended by the 

 air which inflates them ; their diameter in a full-grown larva is 

 about the sixteenth of an inch. 



Dr. Goring states that when these membranes are submitted to 

 examination with the microscope in the usual way, they exhibit 

 the most beautiful specimen of line- work, that it is possible to 

 imagine. The filaments of the upper and under sides, intersecting 

 each other at different angles/'produce an effect which could not 

 be surpassed by the finest and most beautiful engine-turning. 



The orifices by which respiration is performed are at its tail, 

 and each time that it makes an inspiration, it is obliged to ascend 

 to the surface, above which it projects its tail, through the 

 apertures of which it draws in air, until the entire tracheae have 

 been inflated ; thus provided, it sinks again into its proper 

 element, and according as the air thus inspired has changed its 

 character by contact with the blood, and has therefore been 

 rendered unfit for the support of life, it is expelled from the 

 same orifices in the tail at which it entered, and may be seen 

 rising in bubbles to the surface. 



Dr. Goring observes that a comparison of the organs of respira- 

 tion of this insect with those of a caterpillar, affords a beautiful 

 example of the adaptation of their organisation to the elements 

 in which they live. In the case of the caterpillar, every part 

 being constantly exposed to the atmosphere, mouths or orifices 

 lor inhaling the air are arranged along both sides of the body ; 

 while in the aquatic larva, this system could not be made available 

 without compelling the creature to elevate its entire body out of 

 the water, each time it makes an inspiration. The necessity for 

 this is superseded by placing the breathing-mouths in the tail. 



"While admitting the admirable fitness of this arrangement in 

 the two classes of insects, it must not be forgotten, that in the 

 case of the larva of the day-fly, also an aquatic insect, formerly 

 mentioned, the breathing-mouths, according to Dr. Goring's 



85 



