613 



III. Is the remaining system to stand solely because it is the only 

 one left, or can we find positive recommendations for it? 



Is this a case of simply selecting the "most satisfactory hitherto 

 suggested", or is there some standard, reliable as well as impartial, 

 which will testify to absolute rather than relative merit? There are two 

 such standards, of differing values , the one universally acknowledged, 

 the other presented here for the first time within the writer's knowledge. 



a. The former is found in the life-history of the various species, 

 and its testimony, when once accurately presented, is received as final. 



It needed but a partial knowledge of the development of Lernaea 

 to remove it forever from among the worms (Vermes mollusca) where it 

 was first i^laced. The complete life-history we now possess will locate 

 it just as definitely among the Copepoda. 



But unfortunately our knowledge of the life histories of the Cope- 

 pods, especially the parasitic forms, is at present extremely limited. 

 Moreover every investigator who has made the attempt to secure one 

 of these life-histories realizes the extreme difficulty of the task. In a 

 recent number of the Zoologischer Anzeiger (March 16, 1909) Dr. Otto 

 Pesta has called attention to this very fact. He first quotes from 

 G-iesbrecht (1892). "Für eine natürliche Systematik der Parasiten 

 wird es nach meiner Meinung vor allem richtig sein, festzustellen, welche 

 Gruppe der Podoplea die Parasiten sich ausschließen, dann in welchem 

 Cyclopoidstadium bei den einzelnen Arten sich der Beginn des Para- 

 sitismus nachweisen läßt . . . von weiterer Bedeutung für die Gestalt, 

 die der Parasit schließlich annimmt, wird es auch sein, welcher Art die 

 Existenzbedingungen sind, die er an dem Wirte vorfindet" (p. 151). 

 After noting that these suggestions of Giesbrecht's involve difficult 

 and long-continued study, he offers some consolation in the fact that 

 it is not necessary to know the development of every parasitic species 

 in order to lay the foundation of a good classification; it would be 

 sufficient to investigate only the more typical members of the various 

 families. He adds at the close that only when Giesbrecht's proprosed 

 investigations have become actualities will there be hope of establishing 

 a system that will correspond to the natural relationships. But these 

 facts come slowly. Among the true parasites Ave do not at present know 

 the life-history of any genus belonging to the families Ergasilidae, 

 Chondracanthidae , Dichelestiidae and Antheacheridae. We need at 

 least one from each of these; let it be hoped that such an imperative 

 demand will furnish the requisite incentive to some investigator in the 

 near future. 



b. A second standard may be found in a study of the degeneration 

 produced by parasitism, and its testimony is much more easily and 



