V THE HECTOCOTYLUS ARM IN CEPHALOPODA I 39 



entirely introduced within the funnel of the female.' Unfor- 

 tunately the word translated by introduced is corrupt, and can 

 only be restored conjecturally. He again remarks, ' The last of 

 the arms, which tapers to a fine point and is the only whitish 

 arm, it uses in sexual union.' ^ 



The typical hectocotylus seems to have entirely escaped 

 notice until early in the present century, when both Delle Chiaje 

 and Cuvier described it, as detected within the female, as a 

 parasite, the latter under the name of Hectocotylus octopodis 

 Kolliker, in 1845-49, regarded the hectocotylus of Tremoctopus 

 as the entire male animal, and went so far as to discern in it an 

 intestine, heart, and reproductive system. It was not until 1851 

 that the investigations of Verany and Filippi confirmed a 

 suggestion of Dujardin,- while H. Mliller, in 1853, completed the 

 discovery by describing the entire male of Argonauta. 



In all genera of dibranchiate Cephalopoda except Argonauta, 

 Ocythoe, and Tremoctopus, one of the arms is sexually modified in 

 various ways, but never becomes so much prolonged, and is never 

 detached and left with the female. In Loligo Forhesii Stp. the 

 fourth arm on the left has 23 pairs of regularly developed aceta- 

 bula, which then lessen in size and disappear, being replaced by 

 long pedunculated papillae, of which there are about 40 pairs. 

 In Loligo vulgaris Lam. and L. Pleii Orb. 18 or 19 pairs of 

 acetabula are regularly formed, and then occur 40 pairs of papillae, 

 as in Forhesii. In other species of Loligo (gahi Orb., hrevis Bl., 

 hrasiliensis Orb.) only the outer row of suckers becomes modified 

 into papillae after about the 20th to the 22nd pair. In Sepio- 

 teuthis sepioides the modification is the same as in the Loligo 

 last mentioned, but the corresponding arm on the right side is so 

 covered with acetabula towards its extreme end, that it is thought 

 that it in some way co-operates with the hectocotylised left arm. 



In Octopus, the third arm on the right side is subject to 

 modification. This arm is always shorter than the corresponding 

 arm on the other side, and carries fewer suckers, but is furnished 

 at the extreme tip with a peculiar kind of plate, which connects 

 with the membrane at the base of the arm by a channel of skin, 

 which probably conveys the spermatophores up to the tip. 



1 Hist. Anim. v. 6 and 12, iv. 1, ed. Bekker, 1837. 



- ' On pourra constater si ce ne seraient pas des parties detachees de quelque ccplia- 

 lopode dans Ic but de servir h. le fecondation,' Hist. Nat. Helminthes, 1845, p. 482. 



