20 



STRUCTURE OF CEPHALOPODS. 



* 



viscera and is open only in front, (Jig. 8, o). The head issues 

 from this opening : it is round and generally provided with two 

 round eyes, very analogous in their structure to those of verte- 

 brate animals. The mouth occupies the centre : it is armed 

 with two jaws ; and around this opening is found a crown of 

 flexible and fleshy appendages, which are termed, indifferently, 

 legs or arms, because they seem to be entitled to either appella- 

 tion ; for they serve both as organs of prehension and locomo- 

 tion (fi.g. 7). 



3. The cephalopods are essentially aquatic animals, and 

 consequently they breathe by means of branchiae. These 

 organs are always perfectly symmetrical, and are found con- 

 cealed beneath the 

 mantle, in a particu- 

 lar cavity (fig. 8), the. 

 parietes of which alter- 

 nately contract and di- 

 late, and the interior 

 communicates exter- 

 nally by two openings ; 

 one (o) in form of a 

 slit, serving for the 

 entrance of the water, 

 and the other pro- 

 longed in the shape of 

 a tube or funnel (/), 

 serving for the escape 

 of water and excre- 

 ment. Each branchia 

 (6), which is in form 

 of an elongated pyra- 

 mid, the summit of 

 which is directed forward, is composed of a great number of 

 membranous lamella or leaves, placed transversely and fixed 

 on each side of a middle stalk. Each one of these leaves is 

 divided into lamella?, which are in turn again subdivided, and 

 it is in their substance that we find the capillary vessels where 



Fig. 8. BODY OF A POULPE. 



Explanation of Fig. 8. The body of a poulpe seen from beneath (the 

 mantle is slit up on the middle line, and, on one side, raised up to show the 

 interior of the respiratory cavity) : a. the base of the head ; t. the tube 

 by which the water escapes from the respiratory cavity ; o. one of the two 

 lateral openings through which the water enters this cavity ; b. one of the 

 branchiae or gills. 



3. How do cephalopods breathe ? How many branchise have cephalopods 1 



