SEA-FISHERIES LABORATORY. 209 



The Muscular 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 II., 

 fig. 1 and fig. 2). 



The frontal portion of the cephalo-thorax is controlled 

 by two short slender muscles, vtlf., (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 

 supplied with muscles. The antennules have each a pair, 

 which elevate and depress the joints. The grasping 

 action of the antennae 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- 

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