96 Prof. J. Steenstrup on Kectocotyln^-formation 



would prefer naming HyaloteuthiiE or Medusoteuthia ; of the 

 Onychoteuthis group, two, and of the genus Ommatosti-ephes, five 

 species, — yet I have only had a considerable number of indi- 

 viduals of each sex for examination in very few species, namely 

 in one of each of the last-mentioned genera ; so that it is not 

 impossible that an observer more fortunately situated in this 

 respect, and especially one residing on the Mediterranean, might 

 ascertain what I have been unable to discover. In this case, 

 however, the metamorphosis will certainly be confined to an 

 extremely small part of the arm*. 



From the remarkable forms which, as we have seen, are ac- 

 quired by a particular arm in most of the male Cephalopoda of 

 the order Decapoday this being peculiarly developed for a parti- 

 cular object, let us now turn to the Octopoda. If we have been 

 unable to repress the feeling that this remarkable development 

 very closely represents the Hectocotylus-formation in the genera 

 Argonauta and Tremoctopus among the latter, it is natural that we 

 should seek to discover a trace of the same formation in the other 

 genera of the Octopod Cephalopoda, in order, in this way, by 

 closer transitions, to give greater probability to this idea. 



When we investigate the series of the species of the genus 

 Octopus itself, and at the same time compare their external 

 structure, we find that the arm, which is " hectocotylized" in 

 the two genera above mentioned — which, as is well known, is the 



the previously described species by its strong armature of cartilaginous 

 bands on the mantle. Besides a toothed cartilaginous band down the me- 

 dian line of the back, it has on each side of the body two other toothed 

 cartilaginous bands or ribs, which meet at an acute angle exactly at the 

 points where the mantle is united with the funnel on each side ; the pro- 

 portions of the arms are 3, 2, 4, 1, and they only bear two series of suckers ; 

 the tentacles have four rows of suckers on the outer third, which are con- 

 tinued in a scattered arrangement over the middle third ; the fins are ter- 

 minal, small and roundish. Lastly, I have a large and very important 

 species of the same genus from North Greenland, Leachia hyperborea, Stp., 

 which is distinguished from L.pavo, Les., with which it appears to be most 

 nearly allied, by the length of the fins, which are very narrow, follow the 

 sides' of the body for half their length, and together form a lanceolate 

 figure ; by the different comparative lengths of the arms, which are 3, 2, 

 1,4; and by the considerable size of the acetabula and the shortness of 

 the tentacles, which are only twice as long as the true arms. These new 

 species, with several other Cuttle-fishes of the Atlantic, are destined to 

 form the subject of a future memoir. The sixth species is an imperfect 

 Histioteuthis, D'Orb. 



* In my two male Ommatostrephes, Lamk., one of the ventral arms does, 

 indeed, exhibit a ])eculiar form at the apex, which might indicate such a 

 metamorphosis ; but as in one individual it is the left and in the other the 

 right arm, and as both appear to have been slightly injured at this place 

 during life, I could not regard this as normal, especially as I could find 

 nothing similar in male Ommatostrephes of other species. 



