SEA-FISHERIES LABORATORY. 935 
form enlargement is formed. The external nerve gives 
off an abundant series of branches which pass outwards 
to the extreme mantle edge; between external and median, 
and to a less extent between median and internal nerves, 
there are numerous anastomosing branches. These anas- 
tomoses are particularly abundant in the neighbourhood 
of the branching of the common pallial trunks. 
SENSE ORGANS. 
The sensory structures in Cardiwm are :—(1) Sensory 
epithelial cells (Flemming’s cells) in the integument ; 
(2) visual organs borne by the siphonal tentacles; (3) a 
pair of otocysts in the proximal limb of the viscero-pedal 
mass. 
(1) The sensory epithelial cells are found over the general 
body surface, but are more abundant on the mantle edge 
and on the siphons. On the latter they are present in 
groups in the depressions at the free extremities of the 
tentacles borne by the outer wall.* They are either spindle- 
shaped cells with the nucleus at the middle and a bundle 
of long hairs on the free extremity, or elongated cells with 
the nucleus at the base and the free end swollen out into 
a disk, which bears short hairs. Probably they act both 
as tactile and as olfactory organs, the latter function being 
subserved more especially by the cells on the mantle edge 
and siphons. 
(2) The structures generally regarded as visual organs 
(fig. 36, Pl. VI.) are found on the summits of the tentacles 
borne by the outer walls of both siphons. At the free end 
of each tentacle there is a small depression. The lip of 
this depression which faces the siphon is gently rounded, 
*Flemming. Untersuch. u.d. Sinnesepithelien der Mollusken. Archiv 
f. Mikr. Anat. Bd. VI., pp. 439—471, 1870. 
