238 TlMEHRI. 
guished by having the head and thorax fused into one 
and the abdomen generally distinct, by having four 
pairs of legs and never wings on the thoracic part, by the 
absence of limbs from the abdomen, and by the presence 
either of tracheae or of lung-like sacs for respiration. 
(3). The centipedes {Myriapoda) distinguished by the 
head being distin6l from the thorax and abdomen which 
are alike, by the presence of a large number of legs, but 
never wings, on the thorax and abdomen, and by the 
presence of tracheae for respiration. 
Each group is fairly w r ell represented, but as the whole 
collection is in process of renewal and re-arrangement, the 
old specimens havingbeen indiscriminately mixed and much 
damaged through the influence of light, no detailed refer- 
ence to them is advisable. The true insefts occupy nearly 
all the cases ; and all the chief orders are represented. In 
the first case is shewn an index colle6lion, in which typi- 
cal specimens of each order are placed to illustrate the 
classification of inserts, and this will serve as a guide to 
the other cases on the table. Inse6ts are classified 
primarily according to their metamorphoses, or the series 
of more or less marked changes which they pass through 
during development. Thus in the four groups or orders 
of the Butterflies, the Beetles, the Flies, and the Bees, 
the metamorphosis is complete. From the egg is hatched 
out an a6live, vermiform grub, or larva, which eats vora- 
ciously and grows in proportion, changing its skin 
repeatedly ; after a time the larva changes into a very 
different form, the pupa or second stage, when it is 
quiescent unless touched, incapable of changing its place 
or of feeding, and is often fixed to some obje<5t. In cer- 
tain forms, as in the silk-moths, the larva, while changing 
