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 dflue 
colour, and throw out numerous branches at various intervals in 
their course. These tracheae consist of curiously formed fibres, 
binding 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 
for 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 
