108 Prof. J. Steenstrup on Hectocotylns-formation 



I now and then found both large and small portions of a single 

 arm lost, and the wounded surfaces healed. 



From the different forms of the pair of arms metamorphosed 

 for the purpose of reproduction, it appears that there is an un- 

 mistakeable connexion between the position and extent occupied 

 by the metamorphosed part of the arm, and the natural group 

 to which the particular Cephalopod belongs. This appears with 

 peculiar distinctness when the above-described peculiarities are 

 placed in apposition with D'Orbigny's classification of the Ce- 

 phalopoda. 



OCTOPODA*. 



p. •/ V7 J ;t7?""'" ^ 1 ., • 1 T"^* 1 arm a Ilectocotvlus t (femins 

 PmlonexicUe < (Philonexis) > third < > ] ■ a \) ' 



1- Tremoctopus J *■ right J 



OctopidtB-< -pi P }■ third right arm hectocotylized J (feminse monanth'se?). 



Decapoda. 



'Rossia ■) r(with the right one, only in the 



MyopsidcR 



-j \ynia tne r 



[first left arm J middle). 

 I hectocotylized 1 

 Sepiola J (_( alone, in its whole length). 



Sepia I f (at the base). 



Sepioteutkis \ fourth left arm J (at the apex). 

 Loliffo [ hectocotylized | (at the apex). 



Loliolus J L (in its whole length). 



iOmmatostrephes ] 

 Onychoteuthis > No hectocotylized arm hitherto observed. 

 holigopsis J 



* I have not referred here to the Sciadephorus Mnlleri, Eschr. [Cirro- 

 teuthis), a form differing com])letely from the rest of the Cephalopoda. I 

 have certainly examined four males, and found no trace of the formation of 

 the arm indicated in Octopus and Eledone, but I cannot assert with cer- 

 tainty that it would not be found on living examjdes. The peculiar tex- 

 ture of this genus causes all its parts to alter greatly in spirits. As some- 

 thing very remarkable, I must observe, that my four male specimens had, 

 as it were, stripped oiF a portion of the small aoetabula on the lower third 

 of the arm, thus forming small plate-like surfaces, — an appearance which 

 none of my females presented. Whether this might be a sexual character, 

 I am unable to say. The genus appears to form a peculiar family of the 

 Octopoda, although it will be seen, from my present investigations, that it 

 approaches Eledone not only by the single series of acetabula, but also by 

 the cirri which I have indicated at the apex of the arm in Eledone, and 

 which in Sciadephorus appear to represent the greater part of the arm. 



t Deciduous, colourless, developed in a sac. 



X Permanently attached, coloured, developed in a free state. 



serves to be remarked, that whilst as a rule every Octopod has one or two 

 arms reproduced, none of the numerous males wliich I have examined 

 presented this arm in an injured or reproduced state. 



The reproduction takes place with UiUch ease, not only in the direction 



