170 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



this membranous pulley; the operation ceases when it arrives at maturity, and the membrane, 

 being no longer wanted, probably decays. Such is the manner in which our observations lead 

 us to suppose the Nautilus grows; the chambers have certainly no communication with the 

 surrounding fluid. The camerated portion of the shell of Nautilus is evidently a simple, 

 mechanical construction (though planned bj" the wisest intelligence) to assist the specitic gravity 

 of its inhabitant whilst under the difterent mutations of pressure that it is liable to at different 

 periods of growth in its passage through the element; and it is, moreover, a contrivance that 

 could only be effected by the aid of this adjusting membrane upon the simple geometry of 

 motion above described." 



The siphuncle is, therefore, according to this theory, a mechanical contrivance regulating 

 the form of the shell and partially supporting the body during the formation of new septa. 



These theories as to the function of the siphuncle have been gradually discarded as study 

 revealed more of the structure of fossil cephalopod shells and as our morphological conceptions 

 matured. Our present knowledge indicates that the siphuncle is a vestigial structure, having no 

 immediate connection with the ability of the Nautilus to rise or sink. This has been proven by 

 WiLLEY in a series of direct experiments. 



In a communication from New Guinea, in September. 1895, Willey (1896, 1) gives an account 

 of his experiments, as follows: 



"•Being desirous of obtaining, if possible, experimental evidence as to the physiological 

 signiHcance of the siphuncle in the Pearly Nautilus. I have made several successful attempts to 

 cut the siphuncle without otherwise injuring the animal. The evidence supplied by the experi- 

 ment can not be regarded as conclusive, on account of the altered conditions of depth and tem- 

 perature to which the Nautilus is exposed by being brought up to the surface, but it may be well 

 to consider what the results indicate. 



"At tirst I sawed through the shell into one of the chambers, and then cut the siphuncle. 

 This method has the disadvantages of injuriously affecting the efficiency of the chambers and of 

 causing a more or less considerable loss of blood to the animal. The latter will, however, live in 

 confinement about as long as untouched individuals. 



"A young Nautilus operated upon in this way on June 26 was placed in the sea in shallow 

 water for its movements to be watched. It sank slowly to the bottom, and then for a long time 

 made active revolving motions about the vertical axis, but scarcely made any progressive 

 movements. 



"On another occasion (July 10). after several trials, I found that the liest way of performing 

 the operation is to saw through the shell in the neighborhood of the posterior portion of the body 

 of the animal, over the cardiac region, and not to tampei- with the chambers. If the shell be held 

 mouth downward this point lies approximately in the same vertical and transverse plane with 

 the points where the free margin of the mouth of the shell merges into the umbilicus. When a 

 large enough hole has been made in the shell to admit the scissors, the shell being still held upside 

 down, the ventral visceral portion of the body usually detaches itself from the shell, or can be 

 readily caused to do so, and, sinking inward, exposes the root of the siphuncle, which can then 

 be severed. On returning the shell to its normal position the body immediately resumes its 

 normal intimate conta(-t with the wall of the cavity in which it lives, and the pressure so exerted 

 prevents any extensive loss of blood. Under these conditions the operation does not. as a rule, 

 appear to affect the vitality of the animal in any degree. 



"A Nautilus' which was treated in this way on July 10, on being placed in the sea, swam 

 about very vigorously for some time in the middle stratum of water, but most of the time at a 

 little distance from the bottom. On September 13 I operated on four more individuals taken 

 in Talli Bay. on the north coast of the Gazelle peninsula. One of them showed a tendency to 

 sink to the bottom, which it always performed very gradually. In this one I had accidentally 

 punctured the mantle over the heart. The others remained floating and swimming about on the 



' It should perhaps be mentioned that in this particular individual I accidentally cut into the last chamber and 

 plugged the opening with wax. 



