68 
THE BRAIN. 
with its double membrane, like an air cushion, 
which supports and protects this organ. In attempt- 
ing to remove this, only the outer membrane, which 
is thicker and striated, like the tracheae, yields, and 
there remains attached to the brain the lower and 
much thinner membrane, which, like the pia mater., 
sends into the interior its small tracheae, and cannot 
be removed without tearing the brain itself. Thus 
exposed and examined under the microscope, the 
brain substance will be found to consist of transparent 
globules. If some of the hardening liquid is now 
poured on, it does not become uniformly white or 
opaque, but convolutions appear, which are more 
easily studied after prolonged emersion. Regular 
convolutions, more or less distinct, first appear near 
the spot which corresponds to the ocelli. If the 
pulpy substance which covers these convolutions be 
removed, we find the inner substance whiter and more 
solid : this corresponds to the white matter of the 
brain of vertebrates. 
The convolutions form two pairs of discs, turned 
aside and folded, the projecting parts of which are 
swelled like a pad, and the central parts marked with 
radiations. When at last all the surroundings are 
removed, we end by exposing the bodies to which 
these convolutions belong and which Dujardin calls 
pedunculated bodies {corps pedoncures\ These are 
symmetrically arranged in the upper parts of the brain, 
and consist of a short and stout peduncle (stalkf 
bifurcating downwards, ending in two tubercles, and 
bearing the convoluted lobes above them. Of the 
