84 M ERISTIC 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 

 --itiration of the facts is attempted. The evidence of 

 :c 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 

 .m. I body-segments in Peripatns edwardsii varies from 29 to 34 1 : 

 In ! the variation in number must be a manifestation of an 

 original difference in the manner of division or segmentation in 

 tin- progress of development. The change is strictly Meristic or 

 di\ isional. On the other hand, change in number may arise by 

 tli.- Substantive Variation of members of a Meristic series already 

 c. -n-tituted. For example, the evidence will shew that the 

 number of oviducal openings in Astacus may be increased from one 

 I ..ii i to two or even three pairs. Here the numerical variation has 

 come :il..iiit through the assumption by the penultimate and last 

 th.-racic appendages, of a character typically proper to the append- 



- .if the antepenultimate segment of the thorax alone. \ow 

 then- i-, h.-re no change in the number of segments composing the 

 Meristic series, but by Substantive Variation the number of 

 op oings lias been increased. 



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

 to..!. - if 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, 

 \vhi.-h con-i-i in the assumption by one member of a Meristic 

 aeries, of th,- form or characters proper to other members of the 

 - ries, should be recognized as constituting a distinct group of 

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

 and is one "f the ino-t familiar forms of abnormality. MASTERS, in 

 his t r.-at is.- mi Ve^-.-iahie Teratology-, recognizes this phenomenon 

 and gives to ii th<- name .M etam< >r| ih v," adopting the word from 

 i '" ' D< A- Masters says, so long as it is only proposed to use the 

 \\oid m Teratology, no great coiifu.sioii need arise from the fact' 

 that the s.-,ine term and its deri\afi\es are used in a different 

 Jense in several branches of Natural History. Hut if, as I hope, 

 'he time has come \\lien the facts of \\ hat has been called " Tera- 

 \\ill be admitted to their proper place in the Study of 

 Variation, this contusion is ine\itable. In this study, besides, this 

 I'.-iitn-iilar kind of \ariation will be found to be especially impor- 

 l; "it -'"id 1 believe that in the future its significance and the mode 

 of its occurrence \\i|] 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. 



WI( i.. \.. ',""''. Jour. .V/.T. N.-i.. 1 sss, \\vin. p. 4i'>7. 

 i B8, M. I'.. l'. : i,t<il.l,- Ti-r<it<>l,><iii, \>. _':;!. 



