INSEC'TS AND THEIR NEAR RELATIVES,. 
II 
B. Without antennas and with four pairs of legs, although the 
maxillary palpi are often leg-like in form, making the animal 
appear to have five pairs of legs. p. 12. Arachnida. 
BB. With antennae. 
C. With more than three pairs of legs; and without wings, p. 
45.Myriapoda. 
CC. With only three pairs of legs, and usually with wings in 
the adult state, p.48. Hexapoda„ 
Class Crustacea (Crus-ta'ce-a). 
The Crustaceans ( Crus-ta’ce-ans ). 
The members of this class are aquatic Artliropoda, which 
breathe by true gills. They have two pairs of antenncp and at 
least five pairs of legs . 
The most familiar illustrations of the Crustacea are thf* 
Cray-fishes, the Lobsters, 
the Shrimps, and the 
Crabs. Cray-fishes (Fig. 3) 
abound in our brooks, and 
are often improperly called 
Crabs. The Lobsters, the 
Shrimps, and the true 
Crabs live in salt water. 
The Crustaceans are 
distinguished from all oth¬ 
er Arthropods by their 
mode of respiration, being 
the only ones that breathe 
by true gills. Many in¬ 
sects live in water, and 
are furnished with gill-like 
. ,. Fig. 3 —A Cray-fish, 
organs; but these are 
tracheal gills, organs which differ essentially in structure 
from true gills, as described later, in the chapter on Anat¬ 
omy of Insects. The Crustacea also differ from other 
Arthropoda in having two pairs of antennae; and from all 
