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‘ 
THE CEPHALOPODA 329 
along the sides until the most anterior of them reach the mouth 
(Fig. 291), and becoming united in front of it, eventually surround 
it completely. : 
A paired epipodial outgrowth, the origin of the funnel, is formed 
early in development: its two posterior lobes become prominent and 
bend inwards toward one another (Fig. 290, ¢), thus establishing the 
condition which is permanent in the adult Nautilus (Fig. 276), but 
finally, in the Dibranchia, they fuse together completely and form a 
perfect tube. 
All the nervous centres—the cerebral, optic, visceral, and pedal 
—are formed separately as proliferations of the ectoderm. The 
pedal centres give rise, by subdivision, to the ganglia of the arms. 
The eyes (Fig. 292, A, B) and otocysts originate as invaginations 
of the ectoderm, which eventually close up. The otocysts arise 
Fia. 290. 
Development of Loligo. (1) view of the cleavage of the egg during the first formation of 
embryonic cells. (2) lateral view of the egg at a little later stage ; a, limit to which the layer 
of cleavage-cells has spread over the egg; b, portion of the egg as yet uncovered by cleavage- 
cells ; wp, yolk membrane cells; kp, cleavage-pole where first cells were formed. (3) later 
stage, the limit a now extended so as to leave but little of the egg-surface (6) unenclosed ; d, 
eyes; e, mouth; u, mantle sac. (4) later stage, anterior surface, the embryo is becoming 
nipped off from the yolk sac (g). (5) view of an embryo similar to (3) from the cleavage-pole or 
centro-dorsal area. (6) later stage, posterior surface. (7) section in a median sagittal plane 
of an embryo of the same age as (4). (8) viewof the anterior face of an olderembryo. (9) view 
of the posterior face of an embryo of the same age as (8). Letters in (3) to (9) :—a, lateral fins ; 
b, mantle-skirt ; c, supra-ocular invagination to form the ‘‘ white body”; d, the eye; e, the 
mouth ; ep, outer layer of the embryo; f1, f2, f*, f4, f°, the five paired processes (arms) of the 
foot ; g, rhythmically contractile area of the yolk sac; h, dotted line showing internal area 
occupied by yolk; k, first rudiment of the funnel; /, sac of the radula; m, stomach ; mes, 
mesoderm ; n, rudiments of the gills; 0, the otocysts; p, optic ganglion; q, distal portion of 
the ridges which form the funnel; 7, vesicle-like rudiment of the intestine formed independ- 
ently of the parts connected with the mouth; s, rudiment of the salivary gland ; ¢, the closed 
shell sac ; uv, the open shell sac, formed by an uprising ring-like growth of the central dorsal 
area; w, the mantle-skirt commencing to be raised up around the area of the shell sac. (After 
Lankester.) 
laterally on the sides of the foot outside the epipodium (Fig. 290, 
(6), 0); they close up at a relatively late period, often retaining a 
rudiment of the original external canal, and then approach one 
another till they come in contact in the median line. When the 
ocular cavity is closed, the external part of the crystalline lens is 
formed separately from the internal segment. At the sides of 
the optic ganglia a pair of cellular masses, formed by ectodermic 
invaginations, becomes the white bodies of the adult (Fig. 290, ¢) ; 
they are the relics of a pair of embryonic ganglia (lateral cerebral 
lobes). 
The coelomic cavity is hollowed out in the mesoderm as two 
symmetrical spaces, right and left of the intestine ; it gives rise to 
the kidneys and the pericardium. The two kidneys are formed 
independently of one another in their definitive positions. The 
heart is also formed from the pericardial wall as two paired 
‘rudiments. Finally, a portion of the coelomic wall gives rise to 
the gonad. 
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