68 WILLIAM BATESON. 



hypothetical groups has come to be the subject of some ridi- 

 cule, perhaps deserved. But since this is what modern mor- 

 phological criticism in great measure aims at doing, it cannot 

 be altogether profitless to follow this method to its logical 

 conclusions. 



That the results of such criticism must be highly specu- 

 lative, and often liable to grave error, is evident. 



Part I. — The Segmentation of Amphioxus and the Verte- 



BRATA, COMPARED WITH THAT OF THE AnNELIDS. 



From the time when the theory of descent in some form or 

 other became generally accepted amongst zoologists, the ques- 

 tion of the pedigree of the Vertebrates has been the subject of 

 much speculation and controversy. The amount of attention 

 which has been bestowed on this question has perhaps been 

 greater than is warranted by the actual importance of the 

 problem considered as a contribution to general biology ; but 

 when it is borne in mind that the question is that of the history 

 of the human race, the fascination which has been found in it 

 is not surprising. 



Beyond, however, this more sentimental side, there is 

 another source of special interest to be found within the 

 terms of the problem itself; namely, that which is afforded by 

 the obscurity of the solution ; for when the relation of any 

 one group to the rest of the animal kingdom is sought, in most 

 cases there are some cardinal features of anatomy common to 

 it and to some other group, which appear to point to some 

 affinity between them. For example, the structure of the 

 Tracheata at once suggests Crustacean affinities, while there is 

 a strong apparent resemblance between the whole Arthropoda 

 and the Annelids. Even a group so isolated as the Mollusca 

 has points of obvious harmony with other groups as soon as 

 the characters of the Trochosphere are known, and similarly 

 with most other groups. Each and all of these " obvious " 

 resemblances may be illusory, but still they furnish something 



