SEA-FISHERIES LABORATORY. Pip 
inner branchia (Br.I.), which is the larger of the two, is 
narrowest behind where it fuses with the corresponding 
structure of the right side, and increases gradually in 
width towards its anterior margin which is attached to 
the body-wall, and is shghtly overlapped by the labial 
palps. The outer branchia (B7.H.) is narrower than the 
inner, and is broadest at about midway between its two 
extremities. The two branchie of each side fuse together 
behind the viscero-pedal mass at their posterior extrem- 
ities. 
Each branchia consists of a large number of hollow 
filaments connected together at intervals. The direction 
of these filaments is at right angles to the ctenidial base. 
At the free ventral margin, where each branchia is folded 
on itself forming the two lamelle, the filaments of the 
inner pass over with some modification in structure into 
those of the outer lamella. The whole ctenidium is cut 
obliquely to the base in fig. 4, and each of the two 
branchiz is seen to be made up of a direct and a reflected 
lamella. For the greater part, these two lamelle are 
intimately bound together: the precise nature of the 
connections is not, however, shown in the figure. In the 
inner branchia the external lamella (Br.J.1) which is 
inserted into the base of the ctenidium, is the direct one, 
and the internal lamella (Br.I.2) is the reflected one. 
Conversely in the outer branchia, the internal lamella 
(Br.E 1) is the direct one, and the external lamella (Br. 
E.2) 1s the reflected one. This difference in the disposition 
of the two branchia will be noticed, the inner lamelle of 
right and left internal branchie fuse together in the middle 
line, and here the lamelle (67.1.3) are simply mem- 
branous plates, showing no sign of filamentar structure. 
These membranous portions of the inner lamelle are 
continuous at the posterior extremities of the ctenidia 
