MOLLUSCA. 821 



in the gill-sac. Whether an introduction of this organ into the 

 funnel of the female takes place, is not sufficiently cleared up. 



[In certain genera of Cephalopods there is a very remarkable ac- 

 cessory organ of propagation in the males, which we now proceed to 

 notice. Amongst the doubtful genera of Entozoa (p. 188) Hectoco- 

 tylus is recorded. It was first noticed by DELLE CHIAJE in Argo- 

 nauta 1 , and by him referred to the genus Trichocephalus by the 

 name of Trichocephalus acetabularis. Afterwards what was sup- 

 posed to be another species of the same genus was detected in Octo- 

 pus granulosus LAM. by LAURILLARD, and described by CuviER 2 . 

 This presented more than 100 suckers, whereas that of DELLE 

 CHIAJE had only 35, whence it was named by CUVIER Hectocotyle 

 from eicaroRi KoELLiKER 3 , from his examinations of the Hectocotylus 

 of Argonauta, and of another discovered by VERANY in Tremoctopus 

 violaceus, declared it to be the male individual of these animals 

 respectively, and not a parasite. This opinion was afterwards 

 shewn to be unfounded, for YERANY* found in several specimens of 

 a Cephalopod, called by him Octopus Carena (male Oct. granulosus 

 LAM.), that the 3rd arm on the right side was longer and thicker 

 than the rest, and had a bladder at its extremity, whilst PHILIPPI, 

 in a specimen examined by him, saw the same arm fall off on being 

 touched, and found it to resemble exactly the Hectocotylus described 

 by CUVIER, 



At an early period the Hectocotylus arm is developed in its future 

 position in a pediculated vesicle in which it is rolled up. The 

 vesicle alone contains chromatophores 5 . As the development pro- 

 ceeds, the containing vesicle or bladder shews a fissure on that side 

 which is towards the mouth of the Cephalopod from which the hec- 

 tocotylus emerges j but since the latter is attached throughout a con- 

 siderable portion of its length to the inner surface of the other side of 

 the bladder, this last is turned inside out when the hectocotylus has 

 escaped, and continues to be attached to it on its dorsal surface. The 

 structure of the hectocotylus is the same as that already described of 

 the other arms, except that in the central canal is an elongated mus- 

 cular pouch, closed at the near end and terminating in a fine tube, 

 and that there is a filament at the end of the hectocotylus (which has 



1 Memorie, II. p. 225, PL xvi. fig. i. 



2 Ann. des Sc. nat. xvm. 1829, pp. 147 J 5^- 



3 Ann. of Natural History, 1845. 



4 Mollusques mediterraneen*, lere Partie. Genes, 18471854, s. 34 and 126, PL 41. 



5 See p. 824. 



