94 NATURAL HISTORY OF WASPS. 
further inquiries. For the divisions of the frame- 
work have a definite relation to the internal arrange- 
ment of parts, and particularly to the insertion of 
the numerous muscles which are contained within 
the thorax, and, indeed, almost entirely fill its cavity. 
The muscular structure of insects differs from that 
of the higher animals in having no connective tissue 
placed between the different bundles of fibres of 
which the several muscles are composed. This cir- 
cumstance gives great facilities for its microscopical 
examination, for, under pressure, the muscle breaks 
down at once into its constituent fibres, without any 
of that teazing which is so injurious to the structural 
arrangements of the muscles of the Vertebrata. Nor is 
there any connective tissue to fill up the spare room 
between the different muscles; if indeed there be any 
spare room at allin insects. Hach muscular fibre, how- 
ever, has its own investing membrane, or sarcolemma, 
which can be traced, at any point where the fibre 
has been broken or twisted, as distinctly as in some 
fishes whose muscles are familiarly used to display 
the sarcolemma. Again, the important distinction 
between the voluntary muscles which are subservient 
to the will, and the organic or involuntary muscles, 
whose action is reflex and independent of the will, 
apparently follows the same rule in insects as in the 
higher animals. ‘To take the instance before us; the 
little muscles which move the head and legs of the 
wasp, the bulky muscles contained in the side of the 
head, which move the mandibles, and those which 
protrude the stmg are all voluntary, so also—I am 
pained for the reputation of my favourites to say it 
—are those which encircle the poison-bag and inject 
