THE AC A RIDA. 
445 
feeling here and there. The larva perforates the pear leaves from 
beneath, and lives under them, forming gall-like excrescences, but 
which are not true galls ; it has only four legs. After its meta- 
morphosis a perfect insect with eight legs comes forth. 
The Itch Insect, of which a representation is given, is one of 
the Acarida or spiders with unsegmented bodies and palpi, which 
enable them to adhere. It undergoes metamorphoses, and the 
larva has six legs. The female burrows under the skin, and the 
male lives upon the surface of the human body. 
M. Robin states that the mites pass through a series of meta- 
morphoses ; a six-legged larva issuing from the egg becoming 
converted into a nymph, from which the adult mite proceeds. He 
has observed in the mites which attack birds in cages ( Sarcoptidce ) 
a more complicated series of phenomena. In them the males pass 
through four and the females five stages. The egg in issuing from 
the animal has the form of a hexapod larva (six-legged) and is 
followed by a stage of a nymph with eight legs, but without any 
organs of reproduction. These turn into sexual males, which moult 
once, and become perfect, or into females. These are like the 
nymphs, and moult, and produce the perfect female which lays eggs. 
The ticks which stick to so many animals and suck their blood 
are spiders, but in their early life they have some of the charac- 
teristics of true insects. Thus, the moose tick collects upon those 
fine deer when they are in the forests, and irritate them greatly. 
The eggs of this tick, when they are hatched, open like the valves 
of a clam shell, and a six-legged creature comes forth from each. 
