Movements of Detached Portions of Bivalve Molluscs. ] 47 



the inch. The left inner did the same in 14, 13, and 10 

 minutes respectively, thus giving an average rate of 12J 

 minutes to an inch. Both gills travelled horizontally at the 

 regular rate of 2 minutes to the inch. The quickest vertical 

 ascent was made by a right outer gill doing 1 inch in 7 

 minutes. Tlie average rate when turned upside down was 

 2J minutes to the inch. Left inner gil], detached on the 

 evening of the 2nd, was found moving visibly with cilia in 

 active movement on the evening of the 4th, so that in 

 this instance, motion continued for at least 48 hours. 



III. — Mantle-lobes. 



The right and left mantle-lobes are just lateral expansions 

 of the integument, arising dorsally from the body-wall, and 

 attached ventrally to each valve of the shell by the thickened 

 muscular margins, which are pigmented posteriorly and 

 provided with tentacular processes. The inner surface only 

 of the mantle is ciliated, and the direction of the ciliar}^ 

 current is outward and backward. On the thin membranous 

 body of the mantle, the current is towards the exterior, 

 while on the thick muscular margin it is towards the 

 posterior end of the body. The movement is rotatory, for 

 although there is a certain amount of forward movement, it 

 only occurs, as it were, in the course of the rotation. 



The entire left mantle-lobe was detached and placed in 

 water, with its outer or non-ciliated surface uppermost. It 

 began to glide away at once, but soon rotated upon its 

 posterior end, turning towards the cut surface. It completed 

 a round in 4 hours 20 minutes, and the quarter rounds were 

 successively 1 hour 5 minutes, 1 hour 17 minutes, 1 hour 

 21 minutes, and the last in 37 minutes. 



Eight and left mantle-lobes were next taken and divided, 

 each into two portions, the brown tentacular muscular 

 margin being separated from the remainder. The brown 

 marginal portion did not move just at fii'st, but afterwards 

 it travelled considerably. The whitish muscular margin, 

 with the thin body of the mantle-lobe, moved visibly, the 

 muscular margin taking the lead and dragging the rest along. 

 The white and brown portions continued moving the day 

 after being detached, and both were found to be sensitive, 

 though not moving, 48 hours after being detached. The 

 pigmented portion is particularly sensitive to stimulation, 

 readilv responding to the prick of a pin. 



L 2 



