AND THE MALES OF CERTAIN CEPHALOPODS. 143 



which is continued beyond the series of acetabula into a long 

 filiform appendage which we name the " flabellum," and which 

 is ordinarily concealed in an ovate sac which terminates the 

 anterior extremity of this arm. This muscular axis is formed, 

 as M. Kolliker has already very well shown, of three different 

 layers, one of which is longitudinal and the other two circular. 

 In the midst there is a hollow cylindrical space, in which are 

 situated two organs which require the more careful examination, 

 since M. Kolliker has entirely mistaken their nature. One of 

 these organs is a blood-vessel with very delicate and transparent 

 parietes, which runs through the whole length of the muscular 

 axis even in the portion which we have called the flabellum, 

 without any great diminution of its volume. There can be no 

 doubt as to the exact nature of this vessel, which we have many 

 times observed by transmitted light in individuals still living, 

 but in which the movements of the heart were too irregular to 

 allow of our determining the direction in which the current of 

 the blood moved. We could very well distinguish the blood- 

 corpuscles, forming at the time of death irregular masses, which, 

 while the heart yet beat, were agitated more or less distinctly. 

 Unable to make any injection of the few specimens at our com- 

 mand, we could not correctly determine the relations between 

 this vessel occupying the central axis of the muscular cylinder, 

 and the cutaneous vessels which appear upon the whole surface 

 of the arm. We believe, however, that we have seen, towards 

 the anterior extremity of the flabellum, this central vessel giving 

 off lateral branches, which pierce the muscular tube to pass to 

 the external surface and to the skin. The vessel is continued 

 uninterruptedly into the pedicle of the arm, where we were un- 

 able to trace it further. It seems indubitable, however, after 

 what we have just said, that it is the central artery of this ab- 

 normal arm, disposed like the central arteries of the other normal 

 arms. 



The second organ worthy of remark, and which is enclosed 

 in the muscular canal, is the nervous cord formed by as many 

 ganglia as there are acetabula upon the whole length of the arm. 

 The tissues of the living individuals are so transparent, that we 

 can perfectly well distinguish the nervous cord in all the arms 

 of these little males without any dissection, and all the ganglia 



