186 Proceedings of Royal Society of Edinburgh, [march 5 , 
The left and right gills were first experimented upon 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 both gills, inner and outer, move and rotate in the same 
direction, it might be thought that they would keep together 
when once started; but, as the inner ultimately separated itself 
entirely from the outer, it shows that the former possesses greater 
power. 
Proportion by Weight capable of Movement . — Owing to the pre- 
sence of cilia on the parts, about body by weight 
was capable of independent movement. For structure of the gills, 
see K. Holman Peck, Quart. Jour. Micr. Science., 1877. For power 
of imbibition, see Dr Th. W. Engelmann, Jour, of Anat. and Pkys., 
vol. iii. 1868-69. 
The author finds in connection with this that the gill loses three- 
fourths of its weight on drying in the atmosphere. 
Left Gills. — The left gills were detached together and placed in 
liquid, with the inner surface of the inner gill uppermost. They 
soon began to glide along in the direction of the cut surface. The 
anterior end moved quietest and more quickly than the other, and 
covered 1 inch in 10 minutes, while the posterior end had only 
moved f inch. Thus the anterior end moved more than twice as 
quickly as the posterior, at first, the result being that the gills turned 
completely round upon their posterior ends, which moved forwards 
at the same time about f inch from their original position. The 
perpendicular gills thus became horizontal, and the quarter of a 
round was completed in a few minutes less than 2 hours. It is 
the movement of rotation, rather than that of translation, which is 
here attended to (fig. 7, diag. 5). 
Right Gills. — The right gills were also detached together, but in 
such a way that the one was free to move upon the other. In this 
instance the posterior ends remained practically at rest, while the 
anterior ends went round. A quarter round was completed in 1 
hour 14 minutes, when the inner gill began to leave the outer 
(fig. 8). 
The second quarter was performed in 35 minutes, when the inner 
had separated itself from the outer (diag. 6). 
How the two gills separated was rather interesting. The inner 
