i !lll!l I Ritter: Halocynthia jolmsoni n. sp. M 



in truth metamefic to a high degree it' not in fact essentially. 

 Certain it is that under such a view the ascidians, which are 

 usually regarded as non-metameric, at least in their adult stages, 

 would change their status completely and would appear as meris- 

 tic to a truly surprising extent. 



To William Bateson seems to belong the credit of having per- 

 ceived, more clearly than any other biologist of the recent period, 

 that the problem of metamerism is really an aspect of a much 

 larger problem. Although his recognition of merism and distinc- 

 tion between meristic and substantive variation are well known 

 to biologists, it will not be superfluous to quote some of his words 

 touching the point here being emphasized. "Under the term 

 Merism," he says, "I have proposed to include all phenomena of 

 Repetition and Division whenever found and in whatever form 

 occurring, whether in the parts of a body or in the whole. The 

 consequences of the admission of this proposition are consider- 

 able and should be fully realized: for on recognition of the unity 

 of these phenomena it is possible to group together a number of 

 facts whose association will lead to simplification of some morpho- 

 logical conceptions, and to other results of utility." (Bateson 

 '94, p. 28.) Then after speaking of "segmentation" and "meta- 

 merism" as these terms are current in morphology, he continues: 

 "By many morphologists the attempt has been made, either tac- 

 itly or in words, to separate such Metameric Segmentation from 

 n1 her phenomena of Repetition elsewhere occurring." Against 

 such a course Bateson takes a strong stand. But even in doing 

 this he reveals the seeming limitation to his relatively broad 

 grasp of the truths involved. If my own conjectures touching 

 the larger significance of merism be true, and if I read Bateson 's 

 book aright, the limitation to his grasp of the subject is marked 

 by the fact that he viewed it primarily from the standpoint of 

 variation. Following close upon the heels of what has just been 

 quoted he writes: "In order to lay a sound foundation for the 

 study of Meristic Variation these errors must be cleared away, 

 and to do this it is necessary to break down the artificial dis- 

 tinction between the phenomena of Metameric Segmentation and 

 other cases of Repetition of Parts, so that the whole may lie situ 

 in their true relations wi1h each other. When this is done, the 



