324 



THE CEPHALOPODA 



common sheath and provided with a circular glandular area : the 

 eight remaining tentacles of the lobe are unaltered. The modifica- 

 tion usually affects the left side (Fig. 255, p), but it has also been 

 observed on the right. On the side opposite to the spadix the four 

 corresponding tentacles are isolated from the other eight and 

 constitute the so - called antispadix. In the Dibranchia the 

 hectocotylised arm of the Decapoda generally belongs to the last 

 pair, counting from the anterior or dorsal face, that is to say, the 

 fourth pair of true arms, but to the third pair in the Octopoda. 

 In the majority of the Oigopsida it is 

 the left fourth arm that is hectocotylised 

 (Onychoteuthidae, Ommatostrephidae), as 

 is the case in Loligo and Sepia ; in Rossia 

 and Sepiola the fourth left arm is hecto- 

 cotylised and the fourth right partially 

 so ; in Idiosepion and Spirula both arms 

 of the fourth pair are hectocotylised, and 

 in the last named they are contained in 

 a common envelope. In the Octopoda 

 the third left arm of Scaeurgus, the third 

 right arm of Octopus and Eledone, and 

 the second of the right side of Cirrhoteuthis 

 are hectocotylised. In Enoploteuthis, 

 Eledone, and Octopus the extremity of 

 the hectocotylised arm is modified and 

 assumes the shape of a spoon ; in Sepia 

 the base of the arm is affected, the 

 modification consisting in the disappear- 

 ance of the suckers ; in Idiosepion and 

 Rossia and Loliolus the suckers disappear 

 over nearly the whole length of the arm, 

 and in the two first named a longitudinal 

 membrane is developed along its exterior 

 aspect and abundant mucous glands along 

 its internal surface. In some Octopoda 



Male of Ocythoe catenulata, show- fV.p Tip^tnpnHrlieprl arm i ctill mnrp nrn 

 ing the hectocotylised arm, ventral tne nec -OtyllSed arm IS Stl 



view, h, the third arm of the right foundly modified, inasmuch as it is auto- 

 side, or hectocotylus; i, funnel; , ,.,, . , . - , 



t\, t^, p, t\ the first, second, third, tomous. Ims peculiarity is found in 



and fourth arms ; x, the apical sac f i PViilnnpYirljiP nnrl Arormmitirlap Tn 



of the hectocotylus; y, the filament tne .c finonexiaae ana Argonautiaae. 

 which issues from the sac when Qcythoe and Tremoctopus the third right 



development is complete. (From y . f , 



Lankester, after Gegenbaur.) arm is modified (rig. 287, h), in Argonauta 

 the third left ; but in all these genera 



the modified arm constitutes a veritable hectocotylus, that is 

 to say, a caducous organ. This hectocotylus originates, and 

 apparently also is regenerated, in a capsule or cyst in which it 

 lies coiled up on itself: being shielded from the light, it is 



FIG. 287. 



