THE CEPHALOPODA 303 
appears to be an undivided ovoid or globular mass, but it is 
traversed by the oesophagus, and its double origin is further demon- 
strated by the hepatic ducts, which are two in number, in all the 
Dibranchia. In the Decapoda the hepatic ducts are long (Fig. 
268, b.d) and traverse the kidneys ; in the Octopoda they are short. 
In the former sub-order the ducts are covered by the so-called 
“pancreatic” glandular follicles, whose structure is a little different 
from that of the liver (Fig. 268, pn). In the Octopoda these 
follicles are situated only on the initial part of the hepatie ducts 
and are nearly buried in the mass of the true 
liver. Digestion is wholly effected in the 
muscular stomach by the action of the trypsin 
secreted by the liver and by the diastatic 
ferment secreted both by the liver and the 
‘pancreatic ” follicles. 
The intestine is relatively short and of 
uniform diameter. In Nautilus and the Octo- 
poda it is slightly sinuous, but in the Decapoda 
it is straight. The anus is situated in the 
middle line towards the anterior part of the 
pallial cavity (Fig. 272, a), and is often fur- 
nished with lateral valves. With the exception 
of Nautilus, Cirrhoteuthis, Octopus arcticus, and 
O. piscatorum, all the Cephalopoda, including 
the fossil Belemnites, have an ink-sac, consisting 
of a highly-developed rectal caecum developed 
early in embryonic life from the dorsal wall of 
the intestine and opening into the extreme 
terminal part of the rectum. This sac is made epee 
up of a deeper part, or gland proper, the cavity —iimentary canal of 
of which is septate, and a reservoir, into which Ommutostrephes sagittatus ; 
the buccal inass is omitted. 
the glandular part opens by a very small 4, ink-bag; 5, its opening 
¥e , ie : . ll : ll d ] 1 into the rectum; ¢, com- 
orince : t e€ reservoir specia iV we eve Opec mencement of the caecum ; 
in the Decapoda. This ink-sac occupies a some- % SPi@l portion of the 
2 ne ‘ caecum; oe, oesophagus ; 
what superficial position to the side of the %, the stomach opened 
: f : vane: -, - longitudinally; 2, probe 
visceral mass. In some species of Sepiola it is passed through the pylo- 
oI ne aie ; -_., lus. (From lLankester, 
trilobed, two lateral accessory organs being after Home.) : 
joined to it. It extends to the posterior ex- 
tremity of the body in Sepia (Figs. 271, i.s; 272, ¢), and is buried 
in the superficial part of the liver in all the Octopoda except 
Argonawuta. The Cephalopoda are able, at will, to expel the 
secretion contained in the reservoir of this anal gland through the 
funnel, and thus conceal themselves by producing a dense cloud in 
the water. An oxydising diastase, called tyrosinase, is concerned in 
the production of the secretion, the latter being known as melanin. 
? f=) 
2. Circulatory Apparatus.—The Cephalopoda, or at any rate the 
