74 THE VOYAGE OE H.M.S. CHALLENGER. 



Family VI. OcTOPODiDiE, d'Orbigny (em.). 

 OcTOPiDiEj d'Orbigny, 



The subdivision of tlie OctojDoda into smaller groups presents considerable difficulties : 

 Steenstrup and others following him have characterised two considerable groups, 

 according as the suckers are in a single or in several series/ but the importance of this 

 character seems to me overrated. In the first place, the character is one rather of degree 

 than of kind, as may be readily seen from the facts that the proximal suckers in the arm 

 of an Octopus are almost always arranged in a single series, and that the number of 

 suckers so disposed is greater or less according as the arm is bent outwards or inwards. 

 This circumstance and the arrangement of the suckers, not opposite in pairs but in a 

 zigzag line, at once suggest that the two modes of disposition may pass one into the 

 other (see also pp. I^Q, 78). 



Furthermore, glancing at the results of this method of classification, it is seen that 

 Eledone and Octopus are separated from each other, and that the former is united with 

 Cirroteuthis and the latter with Tremoctopus and Argonauta. It is not necessary to 

 recapitulate the points of likeness between the first two genera nor those in which they 

 severally difi'er from the forms with which they are thus brought into contact. Indeed, 

 I do not for the present feel disposed to place Octopus and Eledone in separate families 

 at all, the only conspicuous internal difi'erence between them being that in the latter the 

 eggs are attached each by a separate stalk to the wall of the ovary.''' If it were necessary 

 to break up the Octopjodidse, I should propose rather to separate from them the soft 

 semi-gelatinous forms, such as Bolitcena and Japetella, which in this peculiar con- 

 stitution of their bodies resemble the AUoposidse and Cirroteuthidse (though this may 

 indicate merely analogy not homology), but our knowledge of them is at present too 

 fragmentary to render such a course advisable. 



Octopus, Lamarck. 



This genus continues much the same in general scope as when defined by Lamarck, 

 the only considerable loss it has sustained being the removal of the genus Eledone. 



There is perhaps no other group which presents so many difficulties to the systematist, 

 for no two authorities seem agreed as to the characters which are to be relied ujDon for 

 the purpose of defining species ; it will therefore be advisable to say a few words regarding 

 the principles which have been followed in the present Report. 



The general form and proportions of the body are of some value, though not of much, 

 for the whole consistency is soft, there is no firm internal skeleton to aid in giving a 

 determinate outline, and any one who has watched a living Octopus and seen the mantle 



' Overblik, p. 69 ; Fischer, Man. de Conch., p. 331. 



2 Grant, Edin. New Phil. Journ., vol. ii. p. 317, 1827 ; and Brock, Morplwl. Jahrb., Bd. vi. pp. 283, 284, 1880. 



