116 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



which the cup would be complicated by the addition 

 of five small radial pieces between the basal and the 

 oral ; then should be found forms furnished with 

 five arms, at first short and simple, and later longer 

 and more ramified, and so on. All palaeontologists 

 know how far the geological history of the group is 

 from this theoretical scheme. 



What zoologist could have foreseen from the 

 development of our existing Sea-urchins that the 

 irregular type with bilateral symmetry, was derived 

 from the regular with radiating symmetry, and that 

 this latter proceeded from fossil-ancestors of the 

 Palseoechinida type, with manifold rows of meridian 

 plates ? In the ontogeny of the Ccelenteria, nothing 

 recalls with certainty the anterior existence of the 

 cyaihophyllidce and of the cystiphyllidce.. No em- 

 bryological observation could have allowed us to 

 foresee the existence of the early Graptolites nor 

 of the Stromatopores. No stage of development of 

 the existing Branchiopods recalls the numerous 

 forms, with spiral branchial supports, of the 

 branchiopods of Primary and Secondary times. 



It would be easy to multiply these examples. They 

 will suffice to show what a dim light ontogenic re- 

 searches on existing beings cast on those of the earlier 

 geological periods. From the practical point of view, 

 we may say that the stages of embryonic develop- 

 ment have not been preserved, and that it cannot be 

 expected that they will be discovered in the ter- 

 restrial strata. It might not, perhaps, be so if we 

 were dealing with post-embryonic stages ; but, as 

 regards the Invertebrates at least, the attention of 

 naturalists has been but little drawn to that quarter. 



