THE SCAPHOPODA 199 
flattened and devoid of palps (Fig. 183, VI). Laterally and pos- 
teriorly it is provided with two pouches, and quite at its posterior 
end, on either side of its dorsal surface, are two broad, symmetrical, 
and flattened tentacular lobes (Fig. 183, IV) which appear to be 
homologous with the cephalic lobes of Rhipidoglossa (Fig. 130, II). 
The cephalic filaments or “captacula” (Fig. 181, E) are inserted 
on the margins of these lobes, and when extended, radiate in all 
directions from them (Figs. 182, ca; 183, I). 
These captacula are of unequal length, autotomous, and capable 
of regeneration: they are ciliated, highly contractile, and their 
extremities are swollen and club-shaped, with a small lateral con- 
cavity in each. These organs are in the first instance tactile, but 
also prehensile. The difference in their length is the result of 
their regeneration after being lost. 
The foot has the form of an elongated cylinder, is very 
extensible, and when forcibly projected beyond the aperture of the 
/ 
a a) : ; 
Ife / 4 fae ta vr ee g 
Fic. 182. 
Diagram of the organisation of Dentaliwm, left-side view. a, anus; ca, captacula; ¢.g, 
cerebral ganglion ; f, foot; go, gonad ; in, intestine; k, left kidney ; /a.c, labial commissure ; 
li, liver; m, mouth; 0, orifice leading into the perianal sinus; 0c, oesophagus ; pa, mantle ; 
p-g, pedal ganglion, with otocyst ; pl.g, pleural ganglion ; po, posterior orifice of the mantle ; 
ra, radular sac ; st.g, stomato-gastric ganglion. 
shell, serves as a digging organ. In the Dentaliidae it is pointed 
in front, but has an oblique wing-shaped fold or pleat on either side 
of its free extremity: these two folds are contiguous on the ventral 
but interrupted on the dorsal side. In the Siphonopodidae the foot 
ends in a retractile dise with papillated margins (Fig. 183, VII), and 
in Pulsellum there is a filiform tentacle in the middle of the disc. 
The powerful retractor muscles of the foot form two symmetrical 
bundles inserted far back on the dorsal side of the shell (Fig. 181, ¢) 
II. ANATOMY. 
1. Alimentary Canal.—The non-invaginable proboscis (Fig. 183, 
V, VI) leads directly into a true buccal cavity situated in the trunk 
at the base of the foot (Fig. 182, f). In the interior of this buccal 
cavity there is an azygos dorsal mandible and a ventral radula. The 
radular sac is short, but its muscles and cartilages are powerful 
and form a buccal mass of Jarge size. The radula is short and 
arcuate, with five teeth in each transverse row, the formula being 
