AND THE MALES OF CERTAIN CEPHALOPODS. 129 



form, and has a pedicle equal in size to the base of the arm of 

 the opposite side ; this pedicle carries a larger or smaller oval 

 vesicle (PL I. f. 4.), containing the hectocotyliform arm or the per- 

 fectly developed Hectocotylus itself; this hectocotyliform arm is 

 half as long again as the arms of the fourth pair. All the arms 

 are provided with a double series of acetabula. 



Acetabula : these are large, cylindrical, much excavated, pe- 

 dunculate, and distant from one another (PL I. fig. 3.); they alter- 

 nate from the third, enlarge up to the sixth, and afterwards de- 

 crease progressively as far as the extremity of the arms where 

 they are microscopic. The first pair of arms carries forty- five 

 acetabula ; the second, thirty ; the third, thirty ; the fourth, fifty. 



The Hectocotylus is inserted upon a pedicle from which it is 

 readily detached (PL I. fig.3.) ; it is oval below and narrows towards 

 its extremity, which appears as if truncated ; the internal sur- 

 face is flattened, and its whole contour is beset with a very close 

 series of pedunculated acetabula which are oblique, i. e. have an 

 oval section opening a little upon the inner side. These acetabula 

 are united together by a longitudinal membrane which embraces 

 the whole peduncle, and, with the acetabula, forms a continuous 

 line by passing over at the base upon the inner surface of the 

 arm. Generally a little ovoid sac terminates the Hectocotylus. 

 This sac is transparent, and allows a convoluted cord to be seen 

 through its membrane ; the sac is frequently empty, and then 

 the hectocotyliform arm is terminated by a filament or flabellum 

 almost as long as the arm (PL I. fig. 3.), and which is its conti- 

 nuation. The Hectocotylus carries forty-seven acetabula upon 

 each side. The dorsal part is a little convex upon its base ; this 

 convexity is markedly distinguished by a membranous sac open 

 below (PL I. fig. 3.). 



Interbrachial membrane rudimentary, absent between the 

 lower arms. 



Mouth surrounded by two lips, the internal ciliated, the ex- 

 ternal very delicate. 



Funnel very large, extending far beyond the base of the arms, 

 and measuring three-fourths of the length of the body. Two 

 very large aquiferous apertures, placed at the base of the arms of 

 the fourth pair at the point of attachment of the latero- dorsal 

 portion of the funnel and communicating with the orbital cavity. 

 Excluding the hectocotyliform arm, this Cephalopod is never 



SCIEN. MEM. Mrt, Hist. VOL. I. PART II. 9 



