264 
readily used in connection with the fol- 
lowing description. 
Muscular system. The head is mostly 
filled with conical muscular bundles, at- 
tached by their bases to the upper and 
lateral portions of the posterior two-thirds, 
and to some extent to the upper portion of 
the anterior third of the vault of the head ; 
the apices of these conical masses con- 
verge toward the middle longitudinal line 
of each hemisphere, and then pass 
downward, terminating, in the lower half 
of the head, in a white, glistening, tendi- 
nous cord fully a millimetre long, lying just 
behind the optic nerve and reaching down 
into the mandibles, which they serve to 
close. The extensors of the mandibles 
are attached behind and below the eye- 
specks, and pass directly to the outer 
base of the mandibles, which they enter 
by means of a tendon attached to the in- 
terior wall of the same. ‘The retractors 
of the labrum are slight, flat, muscular 
ribbons, attached at one extremity along 
the whole of its upper interior edge 
and at the other to the facial triangle ; 
the labrum is drawn inwards by a double 
muscle, which starts above from its at- 
tachment along each side of the median 
suture above the facial triangle, and 
passes freely downwards, the muscles of 
the two sides confluent and together 0.38 
mm. broad, diminishing in breadth down- 
ward, and terminating in a single tendon 
attached to the middle of the labrum. 
A band or ribbon, made up of simple, 
longitudinal, parallel muscular fibres, col- 
lected into two contiguous strips, the 
inner the narrower, runs from one end of 
the body to the other, near the skin, be- 
tween the spiracles and the ventral line 
PST CHB; 
of the body ; each is made up of a series 
of bands, one to each segment, extending 
across its entire length, and they are 
permeated by minute tracheal vessels 
running mainly at right angles to the di- 
rection of the fibres; from the anterior 
end of the inner strip of each segment, a 
slender muscular strap runs obliquely to 
the middle of the ventral line of the seg- 
ment. Above the spiracles, on each 
side, are three muscular ribbons, the 
lowermost lying nearer the integument 
than the others, its lower edge touching 
the base of the tracheae. Beneath all 
these longittidinal bands, as seen from 
within, 7. e., lying nearer the integument, 
and at the anterior edge of each segment, 
a narrow transverse belt encircles the 
whole body, passing at the stigmatal line 
over the longitudinal tracheal vessel 
which unites two contiguous spiracles, 
and strapping it to the integument. 
The flexor muscles of the true legs 
originate in the body just beneath the 
origin of the outer of the two longitu- 
dinal muscular ribbons of the ventral 
surface of the body, and extend to the 
opposite wall of the segment. ‘The 
muscles of the prolegs consist of flat 
bands forming a muscular coating to the 
walls of the legs, passing in a direct 
line downward, narrowing as they go; 
they do not cross each other, nor pass 
to opposite sides of the legs, but are en- 
tirely simple. 
Passing now to the muscles attached to 
the internal organs, we find the coating 
of the stomach, which is a mere film, 
overlaid by delicate parallel strips of 
muscular fibres crossing diagonally in 
opposite directions ; besides these there 
