Biological Laboratory, Orr)ioiid College. 141 



can throw any light upon their actions when in organic 

 connection with other parts. 



It was while examining the gills of the sea mussel in the 

 ordinary course for medical students, at the Biological 

 Laboratory, Ormond College, that a clue was obtained to 

 the independent motion of the gills, and afterwards of the 

 other parts as well. At first the movement was thought to 

 be microscopic, only to be determined by a micrometer, but 

 T soon found out that it required the largest of plates to 

 allow free scope to the movements of translation and 

 rotation. 



For convenience, the subject will be considered under a 

 fourfold heading, and in the order named : — 



I. — Labial palps, inner and outer. 



11. — Gills, inner and outer. 



III. — Mantle-lobes. 



IV. -Foot. 



And a further division into four sections is necessary, 

 each dealing with one special part of this particular 

 enquiry : — 



{a) Nature, direction, rate, and duration of movement in 

 each of the above four parts when detached and free to 

 move. 



(6) Bearing of the observed movements on the probable 

 functions of the parts concerned. 



(c) Motive power employed in producing the movement. 



(d) Effects of re-agents, &c., on movement. 



Only the first section will be dealt with now. * 



Before proceeding a step further, it will be necessary to be 

 agreed as to the position from which the moving parts are to 

 be viewed, since it is impossible to have them detached 

 and observed in motion in their natural position. If tlie 

 valves of the shell are separated in the usual way, by 

 inserting a knife at the ventral surface and passing it round 

 the posterior end until the posterior adductor muscle is cut 

 through, then if the two valves are spread out flat, with 

 their pointed ends directed anteriorly, the right and left 

 valves will be just reversed from our own right and 

 left. This is the position from which our observations 



