A STUDY OP METAMERISM. 461 



sion, and the admirable work on which the speculation has 

 been based has been in no degree vitiated by the attempts of 

 the authors to push their conclusions beyond the limits 

 deducible from their immediate results. 



The Coelenterates have formed the basis of Sedgwick's theory 

 (34) of the origin of metamerism. The radial actinian has 

 been worked over into a bilateral metameric form, and all the 

 details of structure of the higher forms (ccelom, nephridia, 

 gill-slits, trachea, &c,) have been evolved from the hypothetical 

 actinian ancestor. Wilson (37) has supported the same view, 

 " but only as a suggestion for further investigation of the 

 facts. ^^ The Turbellaria have been the starting-point of Lang 

 (25) and Meyer (29) ; but each author has described an 

 entirely different course of transition from the flat- worm to 

 the Annelid, 



The Nemertian claims have been pressed forward by 

 Hubrecht (22) and Balfour (2), and hinted at by others. 



The Echiuoderms have proved refractory, yet Wagner^ has 

 made out a possible phylogeny from these to metameric forms, 

 and Haeckel (15) reversing the process, made a star-fish out 

 of five fused Annelids. 



The Euteropneiista, declared unsegmented by Bateson (3) 

 and segmented (32) by the present writer, have been believed, 

 nevertheless, by both authors to throw light upon the problem 

 of metamerism. 



With this divergence of opinion it is not surprising to find 

 as great a divergence of method. In one case a radial form 

 has given the starting-point, in the others a bilateral form. 

 But the ways in which bilateral forms have been transformed 

 into the metameric form have been very different. The budding 

 theory has played perhaps the most conspicuous part. Nearly 

 all of the older writers looked upon segmented forms as 

 animal colonies — Quatrefages, Cuvier, Owen, Duges, Geoffroy- 

 St. Hilaire, Lacaze-Duthier, Herbert Spencer, and Perrier. 

 The same idea is often found in later speculation as well. In 



1 Quoted on the autiioritj of Meyer (29). I have not been able to find 

 the original. 



