APPENDIX. 363 
CLASSIS I. CEPHALOPODA. 
General Observations on the Anatomical Structures of Cepha- 
lopoda. 
THE head, which is situated at the anterior part of the body, pro- 
jects beyond the opening of the sac. The mouth contains a tongue 
bristled with tubercles, which are more or less acute in the different 
genera. The eye is very complicated in its structure ; it 1s formed 
of several membranes, which are covered by a skim which becomes 
transparent in passing under it; it 1s sometimes turned back- 
wards, and sometimes serves to form the eyelash: the eyes are very 
different in their structure from those of vertebrose animals; they 
are nevertheless more perfectly formed for vision than those in any 
other class of animals: the ear consists of a small cavity on each side 
near the brain, and is suspended in a membranaceous sac, which con- 
tains a small stony substance. 
The sac contains all the organs of digestion, circulation, respiration, 
generation, and the gland which secretes the black liquor. On the 
lower and anterior part of the sac is situated the cloaca, which 
is furnished with a valve to prevent water from entering into the 
sac through its cavity: at the base of the cloaca terminates the 
lower intestine and the duct conveying the black liquor from the 
gland which secretes it. The sac is short and oval in Polypus, Ele- 
dona, Sepiola and Cranchia* ; much elongated, more or less acute 
in most of the genera of the Family Loliginide. In all the Order 
Decapoda, the sides are furnished with membranaceous appendages, 
serving them for moving in the water. In Sepia they are very slightly 
prominent, extend nearly the whole length of the body, and do not 
unite behind. In Sepiola they rise abruptly from the middle of the 
sac, and resemble wings: in all the genera in the Family Loliginide, 
they rise above the middle of the sac, unite behind, and in most of 
the European genera they are more or less acutely narrower behind ; 
but m some of the North American and South African genera they 
are either obtuse behind or rounded. 
The branchiz im all the genera, which resemble more or less con- 
torted ferns, are situated at the sides of the sac. 
The organs of circulation consist of three hearts; the ventricle is 
situated near the centre, near the bottom of the sac, and sends the 
* An African genus. 
