90 Prof. J. Steenstrup on Hectocotylus-/orma/eow 



very small or almost entirely evanescent. The former is the 

 case with the two innermost rows, in which the acetabula are 

 extremely low, being scarcely one-sixth of the usual height of 

 the suckers, whilst they are still about a third of their diameter, 

 so that they sit like small depressed saucers fixed on a short thin 

 stalk of the inner surface of the arm ; the latter, on the con- 

 trary, occurs in the two upper rows placed towards the back of 

 the animal, the suckers of which are so small that they may be 

 easily overlooked, when we have not large individuals to examine. 

 On a Cuttle-fish of 11 inches in length they are scarcely more 

 than 0-5 millim. in diameter, and their height is far less. The 

 transformation of the arm, however, does not consist only in the 

 retrogression of these acetabula ; this, in reality, only becomes 

 very striking by the coincidence of two other modifications. 

 Thus the arm becomes much broader at the above-mentioned 

 part, not only by the space between the three upper series of 

 acetabula becoming larger, by which these, so extremely small 

 in themselves, being removed to a greater distance apart, must 

 appear even still more inconsiderable, but also by the membra- 

 nous border, which runs along the outer row of acetabula, and 

 which is rather narrow on the rest of the arm, being considerably 

 developed here, and becoming nearly as broad as the surface of 

 the arm. Then the muscular parts, which, as it were, constitute 

 the roots of the peduncles of the suckers, or from which these 

 peduncles, as it were, originate, have been developed in a pecu- 

 liar way, becoming elevated, lying like oblique beams across the 

 arm, and partially crossing amongst themselves, by which means 

 a quantity of pits are produced, which are particularly deep to- 

 wards the upper margin. Lastly, in these pits and on the par- 

 titions which separate them, the skin has everywhere folded 

 itself into elevated, thin, membranous laminae, which run to- 

 gether into a reticulated form, and give the whole surface of this 

 part of the arm a certain resemblance to the inside of a calPs 

 stomach. This pitted and reticulated structure of the surface, 

 which particularly assists the suckers in escaping from the eye, 

 does not confine itself entirely to the true upper surface of the 

 arm, where it is strongest between the two outer rows of suckers, 

 but also extends itself over the corresponding portion of the lateral 

 margin of the arm. It can hardly be doubted that this peculiar 

 structure has for its object a considerable secretion of mucus; 

 but the elucidation of the particular way in which the trans- 

 ference of the seminal mass to the female can thereby be assisted, 

 must be left for future investigations. The tenth or eleventh 

 sucker in each of the four rows makes its appearance suddenly, 

 with its proper size and shape, and from thence to the apex 

 there is no perceptible dift'crence between this arm and that 



