S4 
THe Muscutar System. 
The muscles moving the appendages and segments of 
the body can be distinctly seen and traced to their 
extremities through the transparent exoskeleton (Plate IT., 
fig. 1 and fig. 2). 
The frontal portion of the cephalo-thorax is controlled 
by two short slender muscles, m//., (Plate II., fig. 2) passing 
postero-laterally from near the lateral edge of the cara- 
pace. They act in depressing the margin so as to produce 
a close attachment to the host. The posterior region of 
the cephalo-thorax is supplied with a number of pairs of 
muscles, some passing forward and others laterally, which 
contract and expand that part of the body. The lateral 
margins are controlled by long muscles passing obliquely 
outwards from the anterior end of the lateral suture. 
The muscles of the fourth thoracic and genital segments 
arise near the median line of the posterior portion of the 
cephalo-thorax, and pass backwards. They produce a 
lateral motion of the posterior parts of the body, and also 
a sort of telescoping contraction which draws the genital 
segment into the cephalo-thorax. The muscles of the 
abdomen arise near the middle of the genital segment 
and pass backwards. They produce a telescoping move- 
ment of the abdomen. 
The various appendages and other organs are also well 
supphed with muscles. The antennules have each a pair, 
which elevate and depress the joints. The grasping 
action of the antennz is produced by muscles passing 
obliquely to the lateral margins. The movements of the 
mouth are controlled by a complicated series of muscles 
passing anteriorly, posteriorly and laterally, all of which 
assist in elevating and depressing it when sucking up 
food. ‘The mandibles are provided with muscles of extra- 
