1865.] DUNCAN — ASIATIC ECHINODEKMATA. 361 



distinct ; so deeply has the hypothesis of the restriction of species to 

 definite areas influenced the judgment. It is evident, however, that 

 direct observations must supersede hypotheses in the study of nature, 

 and that carefully recorded facts are not to be overruled by theore- 

 tical considerations. Nearly every palaeontologist who has studied 

 foreign as well as European fossils, and the majority of those natu- 

 ralists who have had a great scope of observation, determine that 

 the whole truth is not conveyed in the opinions just mentioned, and 

 that although the forms of distant localities are to be referred to the 

 same families, genera, and sections of genera, and that varieties of 

 species replace the species at a distance, stUl species identically the 

 same are found separated by great distances or diffused over great 

 areas. It is quite true that some species are restricted in their vertical 

 and horizontal range ; but others, as Mr. Darwin remarks (Origin of 

 Species, p. 381), " have migrated over vast spaces and have not become 

 greatly or at aU modified." There are numerous examples in many 

 families in all formations, from the Silurian to the Recent, of these 

 wide -wandering and unchanging species, and many more of those 

 which are more or less modified or varied. It is dif&cidt to restrict 

 the notion, of the influence of external physical conditions (in a state 

 of change or not) upon specific variation, within its correct bounds. 

 It is clearly the opinion of those who have decided against the pos- 

 sibility of the great range of species, that these external conditions, 

 such as climate, position in latitude and altitude, moisture, heat, sea- 

 depth, ifec, greatly influence and enhance variation, or prevent it en- 

 tirely. But the great biologist just quoted places the matter in 

 its true light; and his following remarks* apply in the strongest 

 manner to the assemblage of species from Bagh and South-eastern 

 Arabia : — '•' As the variability of each species is an independent 

 property, and will be taken advantage of by natural selection only so 

 far as it profits the individual in its complex struggle for life, so the 

 degree of modification in different species will be no uniform quan- 

 tity. If, for instance, a number of species which stand in direct 

 competition with each other migrate in a body into a new and after- 

 wards isolated country, they wiU be little Uable to modification ; 

 for neither migration nor isolation in themselves can do anything. 

 These principles come into play only by bringing organisms into new 

 relations with each other, and in a less degree with the surround- 

 ing physical conditions." 



The inherent power of variation which exists more or less in all 

 animated beings irrespectively of the influence of external physical 

 conditions, and which is shown, in the simplest form, by the so-called 

 individual differences, is doubtless governed, restricted, and increased 

 by definite laws. Natural selection even acts with varying intensity 

 as the great excitant. So some species are very persistent, others 

 vary more or less, and many are so variable as to be termed poly- 

 morphic. The simultaneous occurrence of persistent and variable 

 species over great areas is a fact, and there is nothing abnormal in 

 it. As the different longevities of species, and also of the individuals 

 * Darwin, op. cif. p. 381. 



