NO. 9 



MUSCULATURE OF THE BLUE CRAB COCHRAN 



II 



order Decapoda shall have been dissected and compared carefully, 

 muscle by muscle. It is quite possible that other genera of crabs may 

 show up interrelationships of muscles that are quite obscure in 

 Calliiicctcs. 



THE FH<ST ANTENNA (aNTENNULE) 



In the blue crab this appendage is similar to that of the shrimp and 

 of the crayfish in regard to its high degree of flexibility. The compara- 

 tively large size of the first segment is due to the presence of a large 

 statocyst to which no muscles are attached, these tissues being entirely 

 sensory in function. The structure of the two flagella in the shrimp 



Mb 24a 26 28 



25a 25b 



Fig. 3. — Dorsal dissection of the first antenna of the blue crab with the deeper 

 muscles laid bare on the right side. 



24a and 24b, musculus promotor I antennae ; 23a and 23b, musculus remotor 

 I antennae; 26, musculus productor2 I antennae; 2/, musculus reductor^ I 

 antennae ; 2S, musculus adductor^ I antennae ; 29, musculus abductor2 I antennae ; 

 .■?o, musculus productors I antennae; jt, nnisculus reductora I antennae; 32, 

 musculus reductor4 I antennae. 



67, statocyst. 



and crayfish, as well as in the blue crab, does not give any support to 

 Huxley's opinion that these flagella represent an endopodite and an 

 exopodite, nor can the joint from which they arise be considered as a 

 modified basipodite. 



24 a, b. Musculus promotor a and b I antennae (fig. 3). — This 

 muscle originates in two places on the posterior border of the aperture 

 that connects the interior of the body with the interior of the antennule. 

 Both parts are attached close together on an infolding of the mem- 

 brane lying beneath the statocyst chamber in the first joint. The 

 promotor raises the first joint, bringing it toward the midline and 

 rotating it slightly in its socket. 



25 a. b. Musculus remotor a and h I antennae (fig. 3). — One part of 

 this short but heavy muscle arises on a round cartilaginous disk on 



