9^ Prof. J. Steenstrup on Hectocotylus-/ormc^fon 



In a male specimen of Octopus niacropus, Risso, or 0. Cuvieri, 

 D^Orb., collected by Professor Eschriclit near Cette, and now 

 handed over to the Zoological Museum of the University, I find 

 the characters so far in agreement with those of O. Groenlandicus, 

 that here also the right arm of the third pair is much shorter 

 than the left one, — the former being not quite 10 inches, whilst 

 the latter is nearly 20 inches in length ; and the right arm is at 

 the same time dilated at the apex into a muscular plate of 13 

 mill, in length, but narrow, which bears no suckers, and is sepa- 

 rated from the sucker bearing part of the arm by an elevated 

 fold. Although the specimen was somewhat flaccid, a tendency 

 of the margins of the terminal plate to bend together like a 

 grasping apparatus was recognized ; but no transverse elevations 

 were to be seen, perhaps only in consequence of the above- 

 mentioned state of preservation. Below this grasping-plate the 

 arm was of the regular construction, with the exception of its 

 stronger muscularity and greater thickness, and the muscular 

 border down the side of the arm. 



Another species of Octopus, also a native of the Mediterra- 

 nean, but which I can by no means regard as a small O. vulgaris, 

 exhibits essentially the same character : the arm is represented 

 of half the natural size, with the border unfolded, in Plate III. 

 fig. 3. The number of transverse ribs in the grasping-plate is 17. 



Besides several species of Octopus, the determination of which 

 I have found impossible from the want of materials for compari- 

 son, I have also examined several male individuals of 0. ruffosvs, 

 Bosc, from the West Indies, likewise a great number of males 

 of O. vulgaris, Lamk., from the Mediterranean, and a male Oc- 

 topus from the coast of Chili, which, from the considerable size 

 of some particular pairs of suckers on the lateral arms, appears 

 to be the well-known O. Foatanianns, D^Orb., of that coast. In 

 all of these I have found that this right arm has a muscular fold 

 of skin along its inner or lower side, destined to form a canal or 

 semicanal for the passage of spermatophora, and that it is fur- 

 nished at the extremity with a small sucker-hke dilatation, 

 which, however, is so inconsiderable that it may easily escape 

 observation, whilst the arm itself is sufficiently distinguished 

 from the opposite one by the above-mentioned rolled-up fold of 

 skin, and by its abbreviation, although it is not thicker, as in 

 the other forms, but appears thinner and more pointed in its 

 outer half than the other arms. I must therefore assume, that 

 in all species of Octopus, without exception, this third arm on 

 the right side is destined for the conveyance of spermatophora. 



I must add, particularly, with regard to Octopus vulgaris, 

 Lamk., that five uncommonly large male individuals examined 

 by me ail have the fourteenth, fifteenth, or sixteenth sucker on 



