146 Transactions of the Royal Society of Victoria. 



The left and right gills were fii'st experimented on as a 

 whole, i.e., taking inner and outer of same side together. 

 Next, inner and outer were observed separately, and lastly, 

 small portions were taken. 



As regards the power of movement possessed by the gills, 

 perhaps, no more striking illustration could be given of it, 

 than the fact, that either a single gill or a small portion of 

 it, can travel along a moist surface even when held vertical, 

 and if the plate is turned upside down, the gill still 

 continues to move. 



Dr. Carpenter, in his well-known work on the microscope, 

 in referring to the ciliary motion exhibited by the gill of 

 the sea mussel under the microscope, has remarked, " Few 

 spectacles are more striking to the unprepared mind, than 

 the exhibition of such wonderful activity as will then 

 become apparent in a body, which to all ordinary observa- 

 tion, is so inert." But if he had only looked beyond his 

 microscope, and applied ordinary observation, he would 

 have seen the spectacle of the moving gill, the wonderful 

 result of the lashing of the cilia. 



It is also remarkable that in a sedentary animal like the 

 mussel, more than one-half of its body by weight, when 

 detached and free to move, is capable of independent 

 motion. I took three mussels of average size, and after 

 allowing them to drain sufficiently, weighed the entii'e body 

 as taken from the shell. Then the gills, mantle-lobes, and 

 labial palps were detached and weighed, and it was found 

 that j^hs of the soft body b}^ weight could move about. 



The movement is both translatory and rotatory. The 

 former being a gliding movement, with the free ventral 

 margin always behind. The direction is always that of the 

 cut surface, and the rotation as a rule, takes place with the 

 posterior end as a pivot. 



As the result of numerous determinations at different 

 times, I have found that the gills, both inner and outer, 

 move at an average rate forward, of two minutes to the 

 inch. They frequently cover an inch in 1 minute, and are 

 sometimes much slower, but on the whole I have found 

 them time after time, in succession, doing an inch 

 in 2 minutes. The average rate for a small piece is 

 the same as for the entire gill. The rate of the vertical 

 ascent is more variable. The right inner gill ascended an 

 inch three times in succession, respectively in 9, 10|^, and 

 11 minutes, thus giving an average of 10 minutes to 



