PREFACE. Vll 



it is only to put their identity beyond fu- 

 ture dispute. It cannot but appear remark- 

 able, that peculiar difficulty should have 

 been experienced here ; that a certain 

 genus should be instituted, and a number 

 of species, all distinguished by individual 

 characteristics, brought under it, which 

 scarcely, in a single instance, demonstrate 

 the place to which they belong. Yet this 

 will appear less surprising, when we reflect 

 that the site of an organ, the most import- 

 ant assuredly, the mojuth, has hitherto 

 been referred to the anterior extremity in 

 all, instead of the middle of the belly, its - 

 general position. 



Although the Observations which occupy 

 these pages lead to very different conclu- 

 sions from what such eminent naturalists 

 as Linnaeus, Cuvier, and perhaps the learn- 

 ed and indefatigable Muller, have endea- 

 voured to deduce for the purpose of sys- 

 tematic arrangement, names so celebrated 

 ought not to be mentioned without the 

 utmost deference. Had the genus Plana-* 

 ria engaged their protracted investigation, 

 the phenomena now exposed would not 

 have remained so long in concealment. 



