EXPLANATORY HYPOTHESES 111 



that the two would be included in the same genus. 

 It follows, therefore, that the modern forms are not 

 of independent origin, but are connected with the 

 ancient ones, and have hardly varied at all since the 

 Cambrian period. 



These three hypotheses may be at once ruled out 

 of court as vague and meaningless. 



Professor Haeckel's hypothesis cannot, in my 

 opinion, be admitted in a scientific discussion, for 

 it does not explain anything. It is like saying that 

 locomotives move in different directions because 

 each has a special mode of motion of its own. If 

 this is not a metaphysical conception, it comes, very 

 near it. 



The pangenesis of Darwin is an attempt to 

 explain heredity and atavism ; but it fails to give 

 an adequate account of variation. Neither does it 

 attempt to shew how new cells arise, and why gem- 

 mules should behave as they are supposed to do. 

 Also it is altogether opposed to what we know about 

 cell division. It also must be dismissed. 



Neither Mr. Galton's stirps, made up of organic 

 units, nor Professor Weismann's determinants, 

 made up of biophores, explain why these units or 

 biophores should always grow into the same ulti- 

 mate shape in the adult. They are described as 

 store-houses of energy, and then left there. The 

 chromosomes may be the sole depositories of the 

 hereditary elements, and no doubt their structure is. 

 very complicated ; but the more complicated it is, the 

 less chance is there of guessing right what that 

 structure is. 



