No. 3-] DESCRIPTION- OF CLEPSIATE PLANA. 409 



who has had any experience in collecting and describing leeches, 

 is a very unsatisfactory guide to identification. We do not find 

 then in these descriptions either a single character or a combi- 

 nation of characters that may not belong to any one of several 

 different species. 



Perhaps the claim might be made that "all these species are 

 apt to be quite variable in character in different localities, as 

 well as at different periods of growth " (Verrill, I.e., p. 6yj). 

 This is undoubtedly true of most of the characters above named. 

 But is it true that the variability is so great and so general that 

 distinctive characters are nowhere to be found, either in the 

 external or the internal organization ? In other words, do the 

 "species" and "varieties" grade into one another so closely 

 as to make it impossible to find really distinctive characters .'' 

 Must we be content with descriptions that only help us to bring 

 together more or less nearly related forms, and give up the 

 attempt to find constant morphological features which may 

 serve as a reliable means of identification ? It must be admitted 

 that most authorities — if we may judge from their descriptions 

 — have taken this view. The result is that we still have no 

 uniform method of describing the Clepsinidae, and very few 

 descriptions that are not more a hindrance than an aid to 

 progress in their classification. This is a simple statement of 

 fact, and not a criticism reflecting upon any particular author's 

 work. Early classifiers of the Hirudinea adopted what now 

 appears to be an altogether inadequate mode of description, but 

 which was perhaps all that the times seemed to require. The 

 example first set by European systematists has naturally enough 

 been followed by later authorities, in this country as well as in 

 others, and no one can be justly reproached for not having fore- 

 seen the necessity of a better system. If, then, I attempt to 

 point out defects of method, and to suggest how they may be 

 improved, I trust no one will find cause for thinking that I 

 am actuated by a spirit of captious criticism, or with any desire 

 to belittle the labors of others. The defects to be pointed out 

 are not the defects of any particular piece of work alone, but 

 rather those of a long-standing and generally received method 

 of describing the Hirudinea. The above descriptions of Clep- 

 sine parasitica are neither the best nor the worst of their kind ; 

 but they are fairly representative, and are here made the sub- 



