NATURAL HISTORY OF THE BAY SCALLOP 
581 
ing that the most lateral of the frontal cilia (in a latero-frontal position) function as 
would typical latero-frontal cilia. Dividing the filamentary tube into frontal and 
L. Br. Ax. 
a. 
Pr. FiL: 
PLl 
/vc. L<t. 
•c/. FiL 
Di. La. 
b. 
Pr. FiL OU. FiL 
d. 
Figure 7. — a, Diagrammatic transsection of gills showing their suspension and position relative to adductor, visceral mass, and 
pallial lobes; 6, longisection through portion of outer demibranch of left gill (transsection of plications and filaments of direct 
lamella (below) and reflected lamella (above)); c, transsection of adjacent ordinary filaments, showing cilia and currents 
produced by lateral cilia; d, superior view of portion of reflected lamella of outer demibranch of left gill (very diagram- 
matic); Add., adductor muscle; Di. La., direct lamella; Ex., exhalant current; F. C., frontal cilia; In., inhalant current; 
I. S., intrafilamentary septum; L. Br. Ax., left branchial axis; L. C., lateral cilia; 0. E. D., outer edge of demibranch; Ord. 
FiL, ordinary filament (in “b” direct (below) and reflected limbs of the same filament); Pli., plications; Pr. Fit., principal 
filament (in “6” direct (below) and reflected limbs of the same filament); R. Br. Ax., right branchial axis; Tip. FiL, united 
tips of filaments (very diagrammatic) 
abfrontal portions is the intrafilamentary septum. The connective spurs are situated 
at frequent, regular intervals at the abfrontal edge. These spurs evidently are highly 
muscular and the filaments somewhat so, as will be discussed more fully later. The 
