110 Prof. J. Steenstrup on Hectocotylus-/orm«^ion 



genus Loliolus in the Z/0%o-family. The justification of the 

 mode here adopted of employing the hectocotyhzed arm as a 

 rule for the natural collocation of the forms, lies in its import- 

 ance for the entire reproduction. It would be inconceivable 

 that the various occurrence of this metamorphosis, sometimes in 

 one, sometimes in the other pair of arms, sometimes on the 

 right and sometimes on the left side, sometimes at the apex and 

 sometimes at the base of the arm, &c., should not give rise to 

 the same number of differences in the mode of fecundation, 

 and in the position and manner in which the seminal mass is 

 placed upon the female ; inasmuch as it appears that the semen 

 is hardly involuntarily or mechanically emitted or poured out 

 upon the eggs, but that this is effected by conscious move- 

 ments. AVhat is furnished us in this respect by simple re- 

 flection, is also confirmed by observation. The seminal mass 

 is actually attached to very different parts, and under veiy 

 different conditions, which 1 propose to describe shortly in an- 

 other memoir, of which I shall here only give the general result, 

 that in the genera Sepia, Sepioteuthis, and Loligo, and therefore 

 in all those which have the left arm metamorphosed, the seminal 

 mass is attached to the lips of the female [inemhrane huccale, 

 D^Orb.), which therefore appear peculiarly equipped for this 

 purpose, whilst I have never found the semen attached to this 

 spot in any other Decapod, but on various parts of the mantle 

 or of the viscera ; for example, in Ommatostrephes, deep in 

 the cavity of the mantle in the median line of the back. For 

 comparison with what has hei'e been stated with regard to Sepia 

 and the LoUgines, it must be remembered that the anatomical 

 examination of the two male specimens of Xautilus* has shown 

 a great difference in the development of the peculiar labial por- 

 tions on the two sides of the animal, whilst nothing of the kind 

 occurs in female individuals. 



Although the external sexual distinctions above referred to have 

 proved to be distinct and important, they have not hitherto been 

 perceived by naturalists ; most of them will at least agree with me 

 in regarding them as such, after reading the preceding. To show 

 more distinctly this deficiency in our present knowledge of the 

 Cephalopoda, it will hardly be superfluous, although I trust that 

 it may be considered quite sufficient for this purpose, to quote 

 two of the most modern assertions relating to this subject ; 

 they are dated in the last and in the present year, and will, in 

 my opinion, completely prove the position of science for the 

 time at which they were written. In the new edition of his 



* Vide Tan der Hoeven in Tijdschrift voor de Wis- en Natuurk. We- 

 tenschappen, I. Deel, 184S, p. ()7-75. pi. 1. fig. 1-3, and Transactions of 

 the Zoological Society, 1850, p. 21-29. pi. 5-8. 



