6l8 A. A. W. HUBBEOHT. 



about of new and endless variations of animal life. And it is 

 irrational^ when we have before us, say one of the lowest 

 Vertebrata, in which nobody will deny the presence of distinct 

 metameric segmentation, to conclude that this metamery must 

 necessarily be in many respects reduced, and that in the an- 

 cestral forms it must have been far more complete, must have 

 stretched forwards along the whole of the head, must have 

 been more forcibly expressed than it is now — in all the cephalic 

 nerves, in the nephridia, the gill-slit, &c. ; — all this on the pre- 

 sumption of the existence of an ancestor so completely and 

 exemplarily segmental as to throw no light on the origin of 

 segmentation and metamery, unless by the aid of Perrier's and 

 Cattaneo's exaggerations. Such conclusions must, however, 

 necessarily be made by those who follow Dohrn's and Semper's 

 lead concerning the phylogeuy of the Chordata. 



Bateson, in taking Balanoglossus as his starting-point, 

 finds the acknowledged points of resemblance in the meta- 

 merous gill-slits, &c., and adds to them important data con- 

 cerning the metamerous ccelomic diverticula. Still, for a 

 general view on the origin of metamery, Balanoglossus 

 oflfers no points that we do not find more strongly represented 

 and more forcibly expressed in the Nemertea. It certainly 

 deserves mention that long before Bateson drew renewed 

 attention to the numerous points of agreement between 

 Balanoglossus and the Chordata, M'lntosh^ had done the 

 same for Balanoglossus and the Nemertea, a separate para- 

 graph of his monograph being devoted to the discussion of 

 these homologies. 



Sedgwick (loc. cit.) holds the unsegmented worms to be 

 wholly " negligeable quantities," at any rate superfluous links 

 in the chain that connects the Chordata with the antecedent 

 Diploblastic stages. In my idea both these authors, valuable 

 as certain of their suggestions are, have not been thoroughly 

 aware of the necessity that, in all discussions on the origin of 

 metameric segmentation, we must attempt to grasp at data 



1 W. M'Intosb, ' A Monograph of British Annelids,' " A. Nemerteans," 

 Ray Society Publications, 1873, 1874. 



