562 CRUSTACEA, 
females are the only bloodsuckers, but they exert their sanguinary ability 
with terrible force. 
On the right hand of the engraving may be seen a large and bold-looking 
fly. This belongs to the family of the CEstrida, and is popularly known by 
the name of BoT-FLy. All these insects are parasitic in or upon animals, 
The larva of this Bot-fly resides in the interior of horses, and is conveyed 
there in a very curious manner. The parent fly deposits her eggs upon the 
hairs near the shoulders of the horse, where the animal is sure to lick them, 
in order to rid itself of the unpleasant feeling caused by agglutinated hairs. 
The eggs are thus conveyed to the stomach, to the 
coats of which organ the larve cling, and there 
remain until they have attained their full growth. 
They then loosen their hold, and are carried, to- 
gether with the food, through the interior of the 
animal, fall to the ground, and immediately begin to 
burrow. They remain underground until they have 
undergone their metamorphoses, and then emerge in 
the shape of the perfect insect. 
The HUMBLE BEE-FLY.—This very curious insect 
HUMBLE BEE-FLY. is found in the early days of spring, and may be 
(Bombylius medius.) seen hovering over the primroses and other spring 
flowers. It feeds in the same manner as the Hum- 
ming-bird Moth, and much resembles that insect in many of its habits. 
CRUSTACEA 
HAVING now completed our brief survey of the Insects, we proceed to the 
CRUSTACEA, a very large class, in which are included the lobsters, crabs, 
shrimps, water-fleas, and a host of other familiar beings. Even the Cirrhi- 
peds, popularly known under the name of Barnacles, are members of this 
Jarge class, and a number of curious animals, which have until lately been 
classed with the spiders, are now ascertained to belong to the Crustacea. 
These beings can be easily separated from the insects on account of their 
general structure, the head and throat being fused into one mass, called tech- 
nically the cephalothorax ; the number of limbs exceeding the sixlegs of the 
insects ; and the mode of breathing, which is by gills, and not by air-tubes, 
The name of Crustacea is sufficiently appropriate, and is given to these 
creatures on account of the hard shelly crust with which their bodies and 
limbs are covered. 
The first section of these creatures are called the Podophthalmata, or 
Stalk-eyed Crustaceans, because their eyes are set upon footstalks. The first 
order is that of the Ten-legged Crustaceans, so called on account of the five 
pairs of legs that are set in each side. These are exclusive of the compli- 
cated apparatus of the mouth, and the jaw-feet which guard its entrance. 
The CRABS are placed first in the list of Crustaceans, and are technically 
called Brachyura, or Short-tailed Crustaceans, because their tails are of com- 
paratively small size, and are tucked under the large shielded body. In the 
preliminary stages, however, the Crabs have tails as proportionately long as 
those of a lobster or a cray-fish. 
As the shelly armour of the Crustaceans is, in most cases, so hard, strong, 
and unyielding, the mode of growth might be considered a problem not very 
easy of solution: for with the Crustaceans the growth continues during 
nearly the whole of life, or at all events for several years after they have 
passed through the various changes to which they are subjected in their im- 
perfect stages of existence, Their increase of size and weight is marvel- 
