236 DISEASES OF INSECTS. 
fixed : when hatched or released — for perhaps they may 
be regarded as foetuses in their amnios rather than eggs 
O DO 
— they cease to be parasitical. Let us admire on this 
occasion, (piously observes this great Entomologist,) the 
different and infinitely varied means by which the Au- 
thor of Nature has endowed animals, particularly in- 
sects, for their propagation and preservation : for it is a 
most extraordinary sight to see eggs grow, and pump as 
it were their nutriment from the body of another living 
animal a . As these mites are fixed to the crust as well as 
its inosculations, they must have some means of forcing 
their nutriment through its pores. 
Another insect, remarkable for its resemblance in some 
respects to the scorpion — called in this country the book- 
crab {Chelifer cancroides\ from its being sometimes found 
in books — occasionally is parasitic upon flies, especially 
the common blue-bottle-fly (Musca vomitoria). They 
adhere to it very pertinaciously under the wings ; and if 
you attempt to disturb them, they run backwards, for- 
wards, or sideways, with equal facility. 
Spiders also are infested by mites. Mr. Briggs once 
found a very small Theridion, to the thorax of which 
were attached four oblong bright scarlet mites, each of 
which was as large as the thorax itself. He afterwards 
met with another spider still smaller, attacked by two of 
these swoln parasites, one of which appeared to him 
nearly equal to the spider in size. This mite was pro- 
bably either Leptus Phalangii, or Astoma parasiticum. 
2. We now come to a perfectly distinct tribe of in- 
sect parasites, which belong to that section or order of 
a De Gcer vii. 144—. 
