138 



THE HECTOCOTYLUS ARM IN CEPHALOPODA 



CHAP. 



pointed at the extreme tip. It is not yet known how the sper- 

 matophores find their way into the hectocotylus, or how the 

 hectocotylus impregnates the ova of the female. The arm thus 

 affected is not alwaj^s the same. In Tremoctopus it is the third 

 of the right side, in the Decapoda the 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, 



Fig. 51. — Male of Ocythoe tuber- 

 culata Raf. {= Philonexis cats- 

 nidatus Fe'r.), jNIediterranean, 

 showing three stages, A, B, 

 and C, in the deveh)pnient 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'lj'. Natural 

 size. From specimens in the 

 British Museum. 



nr^i-e than twenty-two centuries ago, distinctly stated that cer- 

 tain of the arms were modified for sexual purposes. Speaking 

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

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

 the female in having^ what the fishermen call the white sexual 

 orofan on its arm ; ' ag^ain, ' Some say that the male has something 

 of a sexual nature (^alBoLcoSe<; tl) on one of its arms, that on 



