312 THE CEPHALOPODA 



at their cephalic extremities ; they are symmetrically disposed on 

 either side of the rectum (Fig. 272, ?), on the somatic wall of the 

 pallial cavity, and are more or less close to the pallial aperture, 

 being further from the aperture in Ommatostrephes (Oigopsida) than 

 in Sepia (Myopsida). In the Decapoda Myopsida the renal orifices 

 are situated on prominent papillae. 



The excretory products of the Cephalopoda consist, in part at 

 least, of solid concretions, and do not contain uric acid, but chiefly 

 guanin. 



The appendages of the branchial hearts of the Dibranchia (Fig. 

 273, x) correspond morphologically with the pericardial glands of 

 other Mollusca. The glandular investment of the branchial hearts 



is also excretory, experi- 

 ment having shown that it 

 plays the same physiological 

 part as a pericardial gland. 

 4. Nervous System. In 

 all the Cephalopoda the 

 essential parts of the 

 nervous system are cen- 

 tralised in the head, round 

 Pia 27g the initial part of the oeso- 



, ' ' ' _. phagus (Fig. 271, n.c). In 



Diagram of the coelom of a female Octopod, a.s seen * r ,., ,* / 



from the ventral side. a.d, the so-called aquiferous AtautllVS the concentration 



duct; a.p, appendage of the branchial heart; b.h, r f L nprVA /, pn f r pc io IPCC 



branchial heart; ca, capsule of branchial heart; g.c, c ' erve- 



genital coelom (gonocoele); o, ovary; o.d, oviduct ; than in the Dibranchia, each 

 o.flr, oviducal gland ; o.o, oviducal orifice ; r.p, reno- 



pericardial orince. (After Brock.) pair Of Centres With its COm- 



rnissure being represented 



by a ganglionic half-hoop. Of the three half-hoops forming the 

 central nervous system, one, the cerebral, is dorsal, and the two others 

 are continuous with it and ventral. The more anterior ventral half- 

 hoop is the pedal centre, the more posterior the visceral. The pedal 

 centre innervates the funnel and the circumoral appendages, the pedal 

 origin of these organs being demonstrated by this innervation in 

 the adult. In the female each of the two large nerves passing to 

 the interior ventral series of tentacles bears a large ganglion at the 

 point where it breaks up into branches to supply the supposed 

 olfactory or lamellar organ (Fig. 280, x, y). The visceral centre 

 gives off nerves to the mantle, the branchiae, and the viscera, the dis- 

 tribution of these nerves being analogous to that of the Dibranchia 

 described below. Finally, the dorsal or cerebral centre gives off nerves 

 to the eyes, the otocysts, the lips, etc. A labial commissure is also 

 present, arising by a double root (Fig. 279, VIII) from the cerebral 

 centre and passing below the sub-radular organ ; and as is the 

 case in the Polyplacophora, the Aspidobranchia, and the Scaphopoda, 

 the stomato-gastric commissure arises from the labial commissure in 



