PREFACE. Vll 



it is only to put their identity beyond fu- 

 ture dispute. It cannot but appear remark- 

 able, that pecuHar 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 mouth, 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. 



