No. I.] STUDIES ON LIMULUS. 1 1 J 



proximal margin of the second. These muscles move the 

 chela toward and away from the mouth. 



The third joint, or movable blade of the chela, is moved by 

 two muscles, — a large flexor [f.^) arising from the anterior and 

 inner sides of the second joint and inserted upon the ante- 

 rior proximal margin of the third, and a small extensor (e.^) 

 arising from the posterior side of the second joint and inserted 

 upon the posterior proximal margin of the third. By these 

 muscles the third joint is moved at right angles to the move- 

 ments of the other joints of the appendages, and the chela 

 opened and closed. 



The Muscles of the Second, Third, Fourth, and Fifth Append- 

 ages (Text-fig. 2). — As these appendages are very similar in 

 their musculature, the third one may be taken as a type, and 

 the others compared with it. The muscles which move the 

 coxopodite are nine in number. Four plastro-coxals (Text-fig. 2, 

 jaand^ . PI Yjj^ pjg 2, ^i,b,e,anAg^ diXXSQ from the side of the plas- 

 tron and are inserted upon the median half of the entocoxite, 

 two on the anterior side and two on the posterior. The re- 

 maining five (Text-fig. 2, J<^andrf. PI YJJ^ pjg 2, ^<:,d,h-j\^ 2ir\S,Q 



from the haemal side of the carapace and are inserted upon the 

 outer portion of the entocoxite. Two of these, ^"^ and 4'^, or 

 y and j"^, are inserted upon the anterior side, and three, 4^, 4', 

 and 4^', upon the posterior. 



In the second appendage the muscle corresponding to 4'^ is 

 absent or fused with the one corresponding to 4'^. In the sixth 

 appendage there is an extra plastro-coxal muscle, 6^, on the pos- 

 terior side, arising from a point on the plastron much farther 

 forward than the origins of the other plastro-coxals of that 

 appendage. The tergo-plastral muscle corresponding to ^^' is 

 apparently fused with 6\ All of these muscles assist in perform- 

 ing the complicated chewing movements of the coxopodites 

 as well as the forward and backward movements of the legs in 

 walking and swimming. 



The second joint, or basipodite (Text-fig. 2, 2-bas.), is moved 

 by two muscles : a large flexor [f.^) arising from the posterior 

 side of the coxopodite [l-cox.) and inserted on the inner proxi- 

 mal margin of the basipodite ; a smaller extensor {e.^) arising 



