12 
THE STUDY OF INSECTS. 
Fig. 4.— Crustacea : a . Cypris; 6 
Cyclops; c, Daphnia. 
except the Myriapoda in having many (more than four) 
pairs of legs. 
The illustrations named above are the more conspicuous 
members of the class; but many 
other smaller forms abound both in 
the sea and in fresh water. Some of 
the more minute fresh-water forms 
are almost sure to occur in any fresh¬ 
water aquarium. In Figure 4 are 
represented three of these, greatly enlarged. 
Among the Crustacea that live in damp places on 
the Sow-bugs, Oniscidce (O-nis'ci-dae), are most often 1 
seen. These frequently occur about water-soaked 
wood ; and are often mistaken, by students begin¬ 
ning the study of Entomology, for insects or Myria¬ 
pods. Figure 5 represents a Sow-bug. 
On the sea-coast an immense number of forms F sSwlbu£ 
of Crustacea occur. 
land 
Class Arachnida (A-rach'ni-da). 
Scorpions , Harvestmen , Spiders , Mites , and others . 
The members of this class are air-breathing Arthropods, in 
which the head and thorax are grown together , forming a 
cephalothorax , which have four pairs of legs fitted for zvalk- 
mg, and which have no feeler-like antenna . 
The Arachnida abound wherever insects occur, and are 
often mistaken for insects. But they can be easily distin¬ 
guished by the characters given above, even in those cases 
where an exception occurs to some one of them. The more 
important of the exceptions are the following: In the Sol- 
pugida the head is distinct from the thorax; as a rule the 
young of mites have only six legs, but a fourth pair are 
added during growth; and in the gall mites ( Phytoptus ) there 
are only four legs. 
In the Arachnida we find only simple eyes. 
The cephalothorax (ceph-a-lo-tho'rax) bears six pairs of 
