and the Hectocotylus. 493 



M. Filippi having seen this Octopus, made out that this ab- 

 normal arm was the Hectocotylus octopodis of Cuvier, upon which 

 Verany thought himself justified in concluding that the Hecto- 

 cotylus octopodis was nothing more than the deciduous arm of 

 the Octopus, carrying male organs. As for the Hectocotyli of 

 the Argonaut, and of the Tremoctopus, Verany is of opinion that 

 they cannot be arms : so that the question of the nature of the 

 Hectocotyli has become more unsatisfactory than ever. 



In studying the Hectocotyli at Messina in the course of last 

 year, I discovered the true male Argonaut, and I had the satis- 

 faction of being able to trace the connexion which exists between 

 this Argonaut, and the Hectocotylus Argonautce. This last is 

 nothing else than a part of the Argonaut which is developed 

 within a coloured sac, which occupies the place of the third arm 

 of the left side. All the male Argonauts which I have seen are 

 small (not beyond an inch in total length), and shell-less ; in the 

 latter respect resembling the females of this size. 



Their superior arms are not expanded, but are pointed : the 

 sac of which I have just spoken incloses, without exception, a 

 single Hectocotylus, whose enlarged portion is contained within 

 the pedicle and attached at its base, whilst the rest of the body 

 is free and coiled up towards the side on which the suckers are 

 placed. 



As soon as the sac is opened, or becomes cleft by the move- 

 ments of the Hectocotylus, this latter curves back, and at the same 

 time the sac inverts itself (se retourne), and becomes the coloured 

 capsule, described by Koliiker in the back of the detached Hec- 

 tocotylus. 



The Argonaut itself contains a very large testis, whose situ- 

 ation and structure are exactly the same as in the ordinary Octo- 

 poda, and which incloses spermatozoa in different degrees of 

 development. 



The excretory canal of this testis could not be demonstrated 

 in specimens preserved in spirits, which at present are the only 

 ones which have been examined with regard to this point. 



However, it can scarcely be questioned that it debouches into 

 the Hectocotylus, since this always contains in the silvery sac de- 

 scribed by Koliiker, spermatozoa, which often fill also the canal 

 which proceeds from it (ductus deferens, Koliiker) as far as the 

 end of the filiform appendage, which very probably performs the 

 part of a penis. 



It is then proved, that the Hectocotylus is formed upon a male 

 Argonaut, and is nothing else in short than an arm metamor- 

 phosed irregularly. This arm or the Hectocotylus is detached 

 when the seminal fluid formed in the true testicle of the Argo- 

 naut has been deposited in it, and from this moment it enjoys 



