204 LIFE OF PROFESSOR HUXLEY CHAP. X 



effect that the cell is the unit of life in which and through 

 which alone living matter manifests its activities. 



The second was his Croonian Lecture of 1858, 

 " On the Theory of the Vertebrate Skull," in which 

 he demonstrated from the embryological researches 

 of Rathke and others, that after the first step the 

 whole course of development in the segments of the 

 skull proceeded on different lines from that of the 

 vertebral column ; and that Oken's imaginative theory 

 of the skull as modified vertebrae, logically complete 

 down to a strict parallel between the subsidiary head- 

 bones and the limbs attached to the spine, outran the 

 facts of a definite structure common to all vertebrates 

 which he had observed. 1 



With the demolition of Oken's theory fell the 

 superstructure raised by its chief supporter, Owen, 

 " archetype " and all. 



1 " Following up Rathke, he strove to substitute for the then 

 dominant fantastic doctrines of the homologies of the cranial ele- 

 ments advocated by Owen, sounder views based on embryological 

 evidence. He exposed the futility of attempting to regard the 

 skull as a series of segments, in each of which might be recognised 

 all the several parts of a vertebra, and pointed out the errors of 

 trusting to superficial resemblances of shape and position. He 

 showed, by the history of the development of each, that, though 

 both skull and vertebral column are segmented, the one and the 

 other, after an early stage, are fashioned on lines so different as to 

 exclude all possibility of regarding the detailed features of each 

 as mere modifications of a type repeated along the axis of the body. 

 ' The spinal column and the skull start from the same primitive 

 condition, whence they immediately begin to diverge." ' It may be 

 true to say that there is a primitive identity of structure between 

 the spinal or vertebral column and the skull ; but it is no more 

 true that the adult skull is a modified vertebral column than it 

 would be to affirm that the vertebral column is modified skull.' 

 TliLs lecture marked an epoch in England in vertebrate morphology, 



