26 Mr. H. G. Seeley on the Origin 



four series makes a W-like outline when traced externally 

 from the dorsal to the ventral surface, the upper part of the W 

 being towards the animal's head. Here, then, is an immense 

 muscular power, so arranged as to act in many directions. 



Removing the whole of the muscles, we expose the verte- 

 brate skeleton beneath them, and find that each transverse 

 muscular segment corresponds with a transverse osseous seg- 

 ment ; and that the direction of the muscles of the two middle 

 strips of the W coincides with the direction of the dorsal and 

 abdominal processes of the vertebrae, and with the nerves. 

 These middle muscular strips are large compared with the 

 superior and inferior strips ; and in transverse section each 

 often shows, by the method of overlapping, an approach to a 

 concentric arrangement of the constituent muscles in the re- 

 gion of the tail. The forces represented by these muscles are, 

 I believe, precisely such in their distribution and combination 

 as theoretically might have been anticipated. But, before 

 considering the effects of their action, it is to be remarked that 

 the discovery of a notochord among the Tunicata lends strong 

 probability to the supposition that the notochord, which ex- 

 tends beneath the neural chord, is not a product, but one of 

 the original foundations, of the vertebrate plan. But, granting 

 a notochord, it is impossible, without a stretch of imagination, 

 under which the reason gives way, to assume the existence of 

 a mass of muscle like that Avliich makes the great bulk of a 

 fish, and then try to account for its segmented condition, as 

 Mr. Herbert Spencer does, by lateral breaking strains. In 

 nature, so far as I am aware, no such phenomenon exists. 

 And it seems to me as gratuitous to assume the existence of 

 the muscles, in order to have them subsequently segmented 

 by these imaginary lateral strains, produced without any force 

 to produce them, as it is to suppose that the foundation of the 

 vertebral column is laid by breaking strains segmenting the 

 notochord. Before such views can claim to be considered in 

 science, their author is bound to show that an animal is acted 

 upon by lateral forces external to itself, and that an effect of 

 such strains would be to cause the muscular tissues to snap 

 into little short muscles, and that such strains continued would 

 eventually pass through the whole of the animal except its 

 skin and viscera ! In the chapter on growth, we have seen 

 that the consequences of strains would be, not a weakening, 

 but a strengthening of the tissues. 



In the axial part of a fish, a serpent, or indeed in any ani- 

 mal, the successive segments, both of bone and muscle, arc 

 exceedingly similar to each other. Almost at all parts of the 

 trunk two adjacent vertebra can only be distinguished from 



