PLATYHELMINTHES 



ing. The Turbellaria are most closely allied to that great extinct 

 group from which they, the Nemer tinea, Eotifera, and even the 

 Annelids, offer increasingly convincing evidence of having been 

 derived. Many questions relating to the affinities of, or the 

 origin of organs in, the Annelids, resolve themselves into similar 

 questions about the Turbellaria. For these reasons, this group 

 is here dealt with at greater length than the others, the interest 

 of which is of a more special nature. 



The history of our knowledge of the Cestodes dates back to 

 ancient times, as the presence and effects of tape-worms early 

 attracted the attention of physicians. Trematodes are first 

 distinctly referred to in the sixteenth century, while Turbellaria 

 first figure in Trembley's memoir on Hydra (1744). 1 The whole 

 subject of the increase in our knowledge of parasitic Platyhel- 

 minthes is dealt with in the standard work, The Parasites of 

 Man, by Leuckart, 2 and a complete list of references in zoological 

 literature to Cestodes and Trematodes is to be found in Bronn's 

 Thierreich? 0. F. Mtiller 4 and Ehrenberg founded our know- 

 ledge of the Turbellaria, but for a long time the group remained 

 in a most neglected condition. In this country Montagu, G. 

 Johnston, and in Ireland, William Thompson, discovered several 

 marine species, one of which, Planocera folium (from Berwick), 

 has not again been -met with on British shores. Dalyell 5 con- 

 ducted classical researches on the habits of Planarians, and Fara- 

 day 6 made interesting experiments on their power of regenerat- 

 ing lost parts. The credit of assigning the correct interpreta- 

 tion to most of the various organs of fresh-water Planarians 

 belongs to von Baer 7 and Duges, 8 while Mertens 9 effected a 

 similar service for the marine forms, or Polyclads. The minute 

 Ehabdocoels were first successfully investigated and classified by 

 Oscar Schmidt. 10 The great work on this group is, however, the 



1 Mimoires pour servir a lliistoire d. Polypes cVeau douce, Leyden, 1744. 



2 Die Parasiten des Meiischen, 1879 . Engl. Transl. by W. E. Hoyle, i. 1886. 



3 Band 4, by M. Braun. (Mesozoa and Trematoda completed ; Cestoda in progress. ) 



4 Verm. terr. etfluv. . . . succincta Mstoria, 1773 ; Zool. Danica, 1777. 



5 Observations on Planariae, Edinburgh, 1S13. 



6 M. Faraday, "On the Planariae," Medical Gazette, Feb. 1832; and in Edin- 

 burgh New Philosoph. Journal, vol. xiv. 1833, pp. 183-189. 



7 Nov. Act. Acad. Caes. Leop. -Carol, torn. xiii. 1827. 



8 Ann. Sci. Nat.- (Zool.) I. torn. xv. 1828. ; ibid. torn. xxi. 1830. 



9 Mem. Acad. St. Pitersbourg, 5th ser. torn. ii. 1832. 



10 Die rhabdocoelen Turbeilarien des Susswassers. Jena 1848. 



