ON VARIATION. 63 



garter-snake (genus Eutaenia B. and G.). An exami- 

 nation of several hundred individuals of this genus 

 yielded the following results : I found seventeen groups 

 of individuals, which could be said to be completely 

 isolated in characters, with very few exceptions. Eight 

 other groups (species) are probably isolated, but they 

 are not represented by a sufficiently large number of 

 specimens to yield a satisfactory demonstration. Of 

 the seventeen, four species embrace fifteen non-isolated 

 geographical forms (subspecies), besides the typical 

 forms (eight of which are included under the E. sirta- 

 lis); and two others include three color forms easily 

 recognizable, besides the typical ones. Similar phe- 

 nomena are presented in every part of the animal and 

 vegetable kingdoms. 



One of the most instructive natural divisions for 

 the study of taxonomic relations as the result of varia- 

 tion, on account of the simplicity of the relations pre- 

 sented, is the Batrachia Salientia, or the order of Ba- 

 trachia to which belong the toads, frogs, etc. Omitting 

 the very restricted suborders of the Aglossa and Gas- 

 trechmia, the Batrachia Salientia fall into two divi- 

 sions, which differ only in the structure of the lower 

 portion of their scapular arch, or shoulder-girdle. In 

 the one the opposite halves are capable of movements 

 which contract or expand the capacity of the thorax ; 

 in the other the opposite halves abut against each 

 other so as to be incapable of movement, thus pre- 

 serving the size of the thoracic cavity. But during the 

 early stages, the frogs of this division have the mova- 

 ble shoulder-girdle which characterizes those of the 

 other division, the consolidation constituting a modifi- 

 cation superadded in attaining maturity. Further- 

 more, young Salientia are toothless, and one section of 



