2j^ DISCOVERY REPORTS 



water, like other liquids, is only slightly compressible, or, more emphatically, is practically incom- 

 pressible. The coefficient of compressibility of sea water is roughly 44 x io-«, which means that at the 

 depth of a mile— the depth at which Nebaliopsis is known to occur— the density of sea water would only 

 be 1/130 the greater. From this figure a rough computation shows that a specimen such as Nebaliopsis, 

 if lowered to a depth of a mile, would diminish in length by approximately 1/400. Clearly, then, a 

 specimen raised up from i mile would expand by 1/400 of its length, that is, by an imperceptible amount 

 that would be extremely difficult to measure. Obviously such an expansion would lead to nothing like 

 the distension of my specimen F2. 



I have stated that the presence of gas in a specimen, such, for instance, as occurs in the air bladder of 

 a bony fish, would make a considerable difference to the above argument, for a gas, unlike a liquid, is 

 extremely compressible. Now the pressure at a depth of 2000 m. is approximately 200 atm. Hence, if 

 there were a bubble of gas in such a specimen at such a depth it would enlarge to 200 times its original 

 volume by the time it was drawn up to the surface, or roughly a bubble the size of a pin's head at the 

 depth of i^ miles would expand to the size of a pea at the surface. This is a considerable expansion and 

 is of the order that might produce the enlargement which Linder maintains has occurred in the 

 Discovery specimen F2. Is there any reason, therefore, to suppose that gas is produced in the body of 

 Nebaliopsis as it is brought to the surface? It might be argued that as it passes upwards the resulting 

 reduced pressure would cause the dissociation of the oxyhaemocyanin that is presumably present in its 

 blood. But the solubility of a gas is proportional to its pressure, and hence oxygen at 2000 m. is 200 

 times as soluble at the surface. Hence any oxygen which might be set free from the dissociation of the 

 oxyhaemocyanin would immediately go into simple solution. For the sake of argument, however, let us 

 suppose that the dissociation took place so quickly that there was not sufficient time for the oxygen to 

 become dissolved before the animal reached the surface. What would be the result? Most probably the 

 animal would burst under the strain of the sudden expansion inside it and the gas would escape. But 

 if it were able to stand the strain without bursting one thing that is certain is that the oxygen would 

 remain in it as a bubble. Anyone who has handled preserved specimens of Crustacea in spirit knows the 

 difficulty of getting rid of a bubble of air in a specimen once it has got in. In my specimen F 2 there was 

 no bubble of air, as I think my photographs (loc. cit. plate xxxii) established without a doubt. 



As far as I have argued, therefore, I have shown that my specimen of Nebaliopsis could not have 

 expanded as suggested by Linder merely by being relieved of the enormous pressure under which it 

 lived, simply because liquids are almost incompressible, which is the same thing as saying unexpansible. 

 Neither could it have become extended with gas, because there was in fact no gas in the specimen when 

 it reached the surface. My chief argument, however, in refuting Dr Linder's suggestion is the obvious 

 undistorted condition of specimen F2. Naturally, when I first received the specimen I was struck with 

 its bloated appearance, and this caused me to wonder whether it could be abnormal. Directly I examined 

 it ventrally and dorsally, however, I had no hesitation in deciding that it must be undistorted, for it 

 showed the complete ventral chain, of nerve ganglia, and, more striking, the complete tubular heart. 

 I am afraid I assumed that this perfection of the inner organs was so obviously a testimony to the 

 condition of the animal that I did not comment on it in my paper ; I merely relied on the photographs. 

 Now, surely it is practically impossible for the hind part of the cephalothorax to be enlarged without 

 producing an obvious distortion of either the nerve chain or the heart. Certainly if the supposed 

 expansion were caused by an expanding gas bubble (and I have shown that this, however remote, is the 

 only possibility) the expansion would not be bilaterally symmetrical, for the bubble would of necessity 

 lodge to one side of the gut. 



The final demonstration, however, that the Discovery specimen is normal comes from the words of 

 Dr Linder himself. He states (loc. cit. p. 7) that 'a study of sections provides a certain proof. . . 



