20 



STRUCTURE OF CEPHALOPODS. 



viscera and is open only in front, {fig. 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 {fig. 7). 



8. The cephalopods are essentially aquatic animals, and 

 consequently they breathe by means of branchias. 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 ulterior 

 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 

 (/;), which is in form 

 of an elongated pyra- 

 mid, the summit of 

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

 membranous lamellse or leaves, placed transversely and fixed 

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

 divided into lamellas, which are in turn 

 it is in their substance that we find the 



Fig. 8. BODY OF A POULPE. 



IS 



again subdivided, and 

 capillary vessels where 



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

 mantle is slit up on tlie 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 tlie water escapes from the respiratory cavity ; — o. one of the two 

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

 branchiae or gills. 



3. Hov/ do cephalopods breathe ? How many branchiae have cephalopods ? 



