84 MERISTIC VARIATION. [part i. 



As the evidence here presented consists, as yet, only of speci- 

 men chapters in the Natural History of Meristic Variation, and 

 does not offer any comprehensive view of the whole subject, no 

 strict classification of the facts is attempted. The evidence of 

 Meristic Variation relates essentially to the manner in which 

 changes occur in the number of members in Meristic series. Such 

 numerical changes may come about in two ways, which are in some 

 respects distinct from each other. For instance, the number of legs 

 and body-segments in Peripatus edwai^dsii varies from 29 to 34 l : 

 here the variation in number must be a manifestation of an 

 original difference in the manner of division or segmentation in 

 the progress of development. The change is strictly Meristic or 

 divisional. On the other hand, change in number may arise by 

 the Substantive Variation of members of a Meristic series already 

 constituted. For example, the evidence will shew that the 

 number of oviclucal openings in Astacus may be increased from one 

 pair to two or even three pairs. Here the numerical variation has 

 come about through the assumption by the penultimate and last 

 thoracic appendages, of a character typically proper to the append- 

 ages of the antepenultimate segment of the thorax alone. Now 

 there is here no change in the number of segments composing the 

 Meristic series, but by Substantive Variation the number of 

 openings has been increased. 



The case of the modification of the antenna of an insect into a 

 foot, of the eye of a Crustacean into an antenna, of a petal into a 

 stamen, and the like, are examples of the same kind. 



It is desirable and indeed necessary that such Variations, 

 which consist in the assumption by one member of a Meristic 

 series, of the form or characters proper to other members of the 

 series, should be recognized as constituting a distinct group of 

 phenomena. In the case of plants such Variation is very common 

 and is one of the most familiar forms of abnormality. Masters, in 

 his treatise on Vegetable Teratology 2 , recognizes this phenomenon 

 and gives to it the name " Metamorphy," adopting the word from 

 Goethe. As Masters says, so long as it is only proposed to use the 

 word in Teratology, no great confusion need arise from the fact 

 that the same term and its derivatives are used in a different 

 sense in several branches of Natural History. But if, as I hope, 

 the time has come when the facts of what has been called " Tera- 

 tology" will be admitted to their proper place in the Study of 

 Variation, this confusion is inevitable. In this study, besides, this 

 particular kind of variation will be found to be especially impor- 

 tant and I believe that in the future its significance and the mode 

 of its occurrence will become an object of high interest. For this 

 reason it is desirable that the term which denotes it should not 

 lead to misunderstanding, and I think a new term is demanded. 



1 Sedgwick, A., Quart. Jour. Micr. Sci., 1888, xxviii. p. 467. 

 - Masters, M. T., Vegetable Teratology, p. 239. 



