204 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



segmented can hardly be doubted ; but this region of the verte- 

 brates has been so wonderfully altered and specialized that the 

 original segments have been greatl}^ changed, and in some 

 instances may have disappeared. The postauditory region pre- 

 sents the simplest condition ; the tract in front of the ear is 

 much more complex. We can say with great confidence that 

 there are many more than the three somites recognized by 

 Oken ; while with some probability we can say that the number 

 is not far from ten or eleven. In the discussion of the problem 

 the greatest weight should be given to the positive evidence of 

 the m)otomes, since it is probable that segmentation originated 

 in the mesoderm ; next in importance are the cranial nerves, 

 while less weight can be given to gill clefts and their modifi- 

 cations, and even less to the so-called branchial sense organs. 



