DYTISCUS MARGINALIS. THE GREAT WATER BEETLE. 159 
The stomach is the principal organ of digestion, and the food is 
there mixed with the gastric juice. This liquid i is alway s acid while 
digestion is going on, and possesses the same qualities as that of 
higher animals, reducing the aliments into pulp, and finally into 
chyme. The gastric juice is most abundant in those insects which 
live on animal food. The glands which supply this juice are very 
well developed, and may be recognised as tiny blunt projections 
upon the outside of the stomach. 
Having described the full grown male and female beetles, I 
must say a few words about the progeny of this amiable couple. (Fig 
28.) I am afraid that I cannot say much in his favour for beauty, but 
there he is, and you must pass your own opinion. The ladies may 
say that he is positively ugly. If so, I bow to their decision. I 
am afraid that I cannot say much in his favour in any other way. 
I have given you the character of his parents, and he certainly is a 
chip off the old block. As soon as he is hatched from the egg, 
the chief business of his life is eating. | His colour, as you see, is 
almost like that of the muddy bottom of the pond where he 
resides, but the colour adapts itself to the water which he inhabits. 
If he happens to be located in running water, his colour is lighter 
than if he dwells in dark stagnant water ; for there he finds a dark 
sombre hue more to his purpose. He lies on the muddy bottom 
ready to seize anything which comes in his way, and having seized 
it, he proceeds to make a meal of it without leaving his hold. He 
is a regular little crocodile. Now there is one point to which I 
wish to call your attention, and that is to the long sharp mandibles, 
which are more apparent in the larva than in the full grown beetle. 
These mandibles are similar in structure to the poison fangs of a 
serpent, very sharp and having a hair-like tube from the point to 
the base. When he has seized his victim, he keeps his jaws im- 
bedded, and sucks up the nutritious juices with as much gusto asa 
City Alderman of the olden time did his turtle soup. He soon 
gets fat, and changes his coat as before described. After he has 
done this two or three times, he prepares for the change into the 
pupal state. He makes a hole in the bank, forms a sort of cell, 
and then changes into a pupa. The pupal condition varies with 
the season. If it is summer when he betakes himself to the pupal 
form, he emerges as a beetle in a fortnight. But if it is at the fall 
of the year when he retires, the pupal condition lasts till the 
following spring. After the fully developed beetle emerges, its 
coat is of a lighter colour, and requires a few days for the armour 
to become hard; and after this is accomplished, we find the owner 
ready to try a fall with anything that comes in his way. I have 
selected this insect for the lecture to-night, to show what perfection 
of mechanism there is about an obscure creature like a beetle, and 
what a fund of information may be gained by observing insects 
