THE MUSCULATURE OF CHITON. 



LILIAN V. SAMPSON. 



Introduction. 



The study of the musculature of Chiton was begun at the 

 suggestion of Professor Lang at Zurich, and to him and to Dr. 

 Karl Fiedler I am greatly indebted for advice and assistance 

 during the first part of the work : the study was completed 

 under the direction of Professor Morgan, of Bryn Mawr College, 

 who has furnished me with material in addition to that orio-i- 

 nally procured by Professor Lang, and has greatly aided me by 

 his kind interest and assistance. I am glad to have this oppor- 

 tunity to acknowledge Professor McMurrich's kindness in 

 looking over the manuscript. 



The anatomy of Chiton has been carefully worked out by 

 Haller; he has described in detail the digestive tract, the 

 circulatory system, the nervous system, the nephridia, the 

 reproductive system, and also the muscles of the walls of 

 the internal organs. The chief muscles of Chiton are those 

 of the shell, of the foot, of the mantle, and of the radula. 

 The muscles of the shell, foot, and mantle are attached to the 

 shells, and it is therefore important to bear in mind the arrange- 

 ment of the shells. 



On the dorsal side of Chiton are seen the exposed surfaces 

 of eight distinct shells encircled collectively by the mantle. 

 Shells III to VII inclusive (reckoning from anterior to poste- 

 rior) are plates arched over the back of the animal (Fig. i, V); 

 the anterior portion of shell II, which is longer antero-poste- 

 riorly than any of the other shells except the terminal ones, is 

 curved over the anterior end of the body, while shells I and 

 VIII (Fig. I, I and VIII) cover the curved ends of the body 

 to the edge of the mantle where it passes around the ends of 

 the animal. The lower layer of each shell (except I) is con- 

 tinued anteriorly on either side under the shell next in front 



