I 89 J 
CUTTLE-FISHES (Cephalopoda). 
The Cephalopoda include Squids, Cuttle-Fishes and 
Nautili^ and they are all marine. They are bilaterally sym- 
metrical and possess all the parts which above (see p, 78) were 
enumerated as constituting the body of a typical Mollusc. The 
head Is large and bears two eyes which in some species are of 
enormous dimensions. The foot is present too, but has under- 
gone extraordinary modifications. It has been split up into a 
number of tentacles or arms surrounding the mouth. Also the 
mantle is present and forms a spacious cavity containing the 
gills- The communication of this branchial cavity with the 
outside is established by a funnel which may consist either of 
one piece or of two pieces closely applied against each other. 
Thi-s funnel is also derived from the original foot There is, at 
least in most cases, also a radula. As the arms of the Cuttle- 
fishes are derived from the foot, it follows that the mouth with 
the surrounding arms is to be regarded as situated on the 
ventral surface of the body. Dorsal to it is the visceral hump 
of the body, whilst the branchial cavity with the funnel is 
situated posteriorly. 
A proper external shell, formed by the mantle, is found in 
Nautilus only. The shell of -the Paper-Nautilus (Argonauta 
nrgo) is formed by the female only and is secreted not by the 
mantle, but by the two dorsal arms of the animal. It serves in 
the first instance as receptacle for the eggs, though the mother 
Argonauta can retreat in it as well.^The shell ot Spiruta is very 
small compared with the body of the animal, it is of the shape 
of a ram's horn and almost entirely internal. In the other 
Cephalopods the shell is much reduced or may be nearly obso- 
lete and is covered over with the mantle. These internal shells 
are fiat and straight and consist of calcareous or horny matter. 
All Cephalopods, with the exception of the Nautiius, 
possess an ink bag. It opens into the same funnel from which 
the respiratory water is expelled, and the inky fluid discharged 
ts probably a means of defence, enabling the animal to make 
itself invisible to pursuing enemies. Cuttle-fishes progress by 
walking with their arms and by swimming. The swimming is 
effected by the expulsion of water from the funnel. In intel- 
ligence they stand far above the other Molluscs. 
The Cephalopods are divided into two principal groups 
according to the number of their gills, viz. into Teifabranchia, 
with four gills, and Dibranchia, with two gills. 
