320
J. H. 9. BLAXTER AND F. 0 . T. HOLLIDAY
line. It may be that a complex head lateral line is found in other
shoaling species and plays some part in maintaining the shoaling, though
dght seems to be the more dominant sense. It has also been put forward that the lateral line could play a part in proprioception, particularly in relation to swimming.
I
0.p.l.
h.c.1.
Fro. 11. T h e lateral line ayatem on the head of a herring 50 mm long, u p p r jaw in dark
outline. (Reproduced with permimian from Iknforrl, 1 V4 1.)
BD
= anterior commiasure
nos = noatril
hcl = horizontal cheek line
ptu = posterior tubule
pdi = posterior dilatation
cpl :
= central pit lirro
mpl = middle pit line
~ t c - nupra ternrmrrrl wmnl
opl r tmcil pit linu
N. Buoyancy a d equilibrium
1. Buoyancy
Tho suaclonal variation in fat aonthnt of clupoids means also 8
seasonal variation in tissue density (Jones and Marshall, 1053). The
distribution of fat in herring is such that the fish will remain on an even
keel, the centre of gravity ” of fat distribution being just anterior to
the dorsal fin (Brandes and Dietrich, 1963a; Love, 1957). It seems
likely that there is an abrupt change of density of body tissue at