138 



THE HECTOCOTYLUS ARM IN CEPHALOPODA 



into the hectocotylus, or how tlie liectocotyhis impregnates the 

 ova of the female. The arm thns affected is not always the 

 same. In Tremoctopus it is the third of the right side, in the 

 Dccapoda tlie modification usually affects the fourth of the left. 



This singular property of the male Cephalopoda has only 

 recently been satisfactorily explained. It is true that Aristotle, 

 more than twenty-two centuries ago, distinctly stated that certain 



Fig. T<\ . — Male of Onjthoc iuhercu- 

 lataRaf. ( = Philonexis catenu- 

 latus, Fer. ), Mediterranean, 

 showing three stages, A, B, 

 and C, iu the deveh)pment of 

 the hectocotylus arm: h.cy, 

 hectocotylus still in the cyst ; 

 c'y', spoon-shaped cyst at the 

 end of the arm when freed ; 

 th, thread-like organ freed by 

 the rupture of c'y'. Natural 

 size. From specimens in the 

 British Museum. 



of the arms were modified for sexual purposes. Speaking of 

 what he calls the polypus (which appears to represent the Octojins 

 indgaris of the Mediterranean), he says : ' It differs from the 

 female in having what the fishermen call the white sexual organ 

 on its arm ; ' again, ' Some say that the male has something of a 

 sexual nature {alhoLwhh rt) on one of its arms, that on which 

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

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



