DARWIN VS. GALIANI. 



415 



views, but that they should follow even in his further conquests the 

 great leader who by a single blow won the victory for their side. But 

 the end which he points out to us is high above the doctrine of descent, 

 which doctrine, in so far as it attempts to explain the evolution of or- 

 ganic nature solely by its laws of development, is in fact still of little 

 avail to us. 



We must remark, in the first place, that what morphologists denomi- 

 nate laws are not laws at all in the sense of theoretical science. These 

 so-called laws are simply rules deduced from a greater or less number 

 of cases, and like grammatical rules only serve to classify and explain, 

 by a process of vicious circle-reasoning, other facts embraced within the 

 same definition. Even Kepler's laws were but rules of this kind, until 

 Newton deduced them from the universal law of gravitation, and so 

 raised them to the dignity of laws. But now that they are firmly based 

 on the principle of gravitation, the whole doctrine of the movements 

 of the heavenly bodies may be inferred from Kepler's laws with the 

 highest attainable degree of certitude; and our longing to know the causes 

 of things is as fully appeased by this explanation as the nature of the 

 human understanding will permit. We know, with that kind of certitude 

 which we denominate absolute, that, like the planets of our own solar 

 system, so those of unseen suns move in ellipses whose radii vectores 

 describe equal areas in equal times, and that the squares of their revolu- 

 tion times are as the cubes of their distances from their suns. 



It is very different Avith the laws of organic structure. If in a Juras- 

 sic rock we find a fragment of a rhombic enameled scale, we infer with 

 a very high degree of probability that the fish of whose panoply this 

 scale was a part thousands of years ago had an independently pulsating 

 aorta-peduncle. If on breaking up a shapeless piece of fossil bone we 

 discover a spiral auditory cochlea, we know that the animal of whose 

 skull the fragment was a part was a mammal. It is no small triumph 

 that we dare make such assertions as these. Still, there is not absolute 

 certitude here. Even the most firmly established laws of organic struc- 

 ture possess only a greater or less probability. Absolute characters are 

 in systematics the philosopher's stone. True, in some cases the prob- 

 ability grounded on laws of organic development borders on certitude. 

 That we shall never find a centaur, pegasus, griffin, a configuration like 

 that of an angel or a demon, whether living or fossil, we may affirm 

 with almost the same certainty as that a planet which has never been 

 observed will obey the laws of Kepler. Whether we can with equal 

 certitude affirm that never will a vertebrate be found in which by a 

 transposition of the central nervous sj'stem the posterior and the an- 

 terior roots of the spinal-cord nerves will have interchanged functions, 

 may perhaps be open to doubt, however improbable such a thing may 

 be. Would the comparative anatomist ever have supposed a priori 

 that such a structure could exist as that of the PleuronectCB ? Then, 

 in the Invertebrata the uncertainty of the laws of organic structure is 



