THE HECTOCOTYLUS ARM IN CEPHALOPODA 139 



which the largest suckers occur ; that this is a kind of muscular 

 appendage attached to the middle of the arm, and that it is en- 

 tirely introduced within the funnel of the female ' Unfortu- 

 nately 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 intes- 

 tine, heart, and reproductive system. It. was not until 1851 that 

 the investigations of Verany and Filippi confirmed a suggestion 

 of Dujardin,^ while H. Miiller, in 1853, completed the discovery 

 by describing the entire male of Argonauta. 



In all genera of dibranchiate Cephalopoda except Argonauta^ 

 Ocythoe^ and TremoctopuSy 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 

 acetabula, 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 be- 

 comes 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 hec- 

 tocotylised left arm. 



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

 ification. This arm is always shorter than the corresponding 

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



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



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

 c^phalopode dans le but de servir a le fecondation,' Hist. Nat. Hehninthes, 1845, 

 p. 482. 



