818 
1 
CLASS XIII. 
the cerebral ganglion, the lowest contains the auditory organs, and 
the lateral parts, broad and excavated like a cup, receive the eyes. 
The orbits are guarded in front by two elongated cartilaginous plates, 
which are attached by their base to the cartilaginous ring and else- 
where are extended freely over those cavities. In the Sepia there is 
an additional triangular cartilage, of which the point is attached to the 
ring, the base turned towards the arms, and tv which the muscles 
of the arms are affixed. In Sepia and Loligo there are further 
found two catilaginous plates on the back, and, on each side of the 
body, an elongated flat cartilage which supports the lateral expan- 
sions of the mantle or the fins’. In the Mauttlus there is only one 
cartilage present in the head, which lies beneath the cesophagus, but 
does not enclose this annularly, and is prolonged on each side to the 
funnel. The eyes, which in this genus are placed on pedicles at the 
side of the head, are not protected by this cartilage. 
The head of these molluscs is round and broad and separated by 
a constriction, as by a neck, from the body. Around the mouth are 
placed in most eight or ten arms; in Nautilus, on the contrary, 
several membranous sheath-like appendages, perforated internally, 
in which thin cylindrical tentacles, capable of extension and retrac- 
tion, are inclosed. Where eight or ten arms are present, eight of 
them have constantly a somewhat conical form and stand in a circle 
round the mouth. On the upper surface, that which faces towards 
the mouth, these eight arms are covered with numerous suckers, by 
which they attach themselves to different bodies. (In the ten-armed 
two are placed on the outside beyond the circle of the other eight on 
the ventral surface, and can by retortion be drawn entirely within 
the body. Already had Arisrorie distinguished these two from the 
other arms under the name of proboscides.) The arms are hollow 
internally, for the passage of the artery and nerve; radiating mus- 
cular fibres run from the middle outwards, and on the surface is a 
layer of circular and longitudinal muscular fibres, by which all the 
various motions of retraction, contraction, flexure and convolution 
become possible, which, on the seizure of prey, are executed by 
these organs. 
Under the head is situated a conical organ, which is open at the 
extremity, the funnel (infundibulum) formed by an extension of the 
mantle and provided with muscular walls. In Nautilus it has two 
See C. A. Scuuttze in MecKEt’s Archiv fiir die Physiologie, tv. 1818, 8. 334— 
338, Tab. Iv. fig. 1. 
