278 NATURAL SCIENCE. Oct., 



pre-Darwinian statement that the ala spuria is "analogous to the 

 thumb," while the other two digits are called simply "second" and 

 " third," that is second and third digits not of the pentadactyle but of 

 the tridactyle fore limb. Such phrases in works written on the then 

 undoubted hypotheses of special creation and of fixity of species, could, 

 obviously, not mean that the three digits called "thumb" and 

 "second" and "third" digits had been evolved from the digits 

 I, II, and III of the pentadactyle fore limb of an ancestor: the 

 authors did not believe birds had ever had such ancestors. The 

 transcription of such phrases into post-Darwinian treatises, without 

 consideration of the new meaning which they would thus gain from 

 the new context, appears to have been the origin of the error. 



And yet Professor Huxley (5) has relied upon the unfounded 

 statement that these digits are I, II, and III in constructing a theory 

 of the phylogeny of birds. On the strength of this assumption he 

 has denied the descent of birds from Pterodactyles. They may, of 

 course, not be so descended, but we may not reasonably believe that 

 his argument from the wing-structure makes their descent one jot 

 more improbable than it was before. 



It may at least be said that, in the matter of pelvis and of wing, 

 Avchaoptcryx is much more like a Pterodactyle than it is like 

 Compsognatlius, or any other Dinosaur. 



Those " ornithic " characters of the Dinosaurs which distinguish 

 them from Pterodactyles, distinguish them also from the undoubted 

 bird Archcroptcry.x; and if the "ornithic" characters of the Dinosaur 

 pelvis generally, and of the foot of Compsognatlius, are due to any blood- 

 relationship with birds at all, it seems probable that the phylogenetic 

 tree will have to be turned upside down so as to express the descent 

 of Dinosaurs from Carinate birds through a series of " ratite " birds 

 which had lost the power of flight through isolation and consequent 

 suspension of the action of a selection dependent on powers of flight, 

 much as the existing " Ratitae " have probably descended from 

 Carinates of very various orders. 



It is, however, not to put forward new phylogenies that I now 

 write, nor merely to correct a particular error in biological theory, 

 but to point to one of the most fruitful sources of error. 



To attempt to expose one by one all the current biological errors 

 would be very much like going to Mecca, armed with a microscope, 

 in order to eradicate cholera by finding the bacilli, and killing them 

 one by one as they were found. 



With reference to cholera epidemics, it has been said, "Cholera 

 is a filth-disease: abolish filth, and cholera will vanish." 



Uncritical credulity plays the same part in the spread of error asfilth 

 plays in the spread of cholera. The standard text-book of the anatomy 

 oftheVertebrata (6) says, "In all Carinatae there are three digits in the 

 manus, which answer to the pollex, and the second and third digits 

 of the pentadactyle fore limb " ; and the statement is not accompanied 



