THE PLATYHELMIA 



THE group of " Flat worms " constitutes one of the phyla of 

 the Metazoa. Linnaeus associated Lumbricus with the various 

 worms which are now known as Flukes, Tapeworms, Nemertines, 

 Nematodes, and Leeches in the order " Intestina," which he 

 placed close to his heterogeneous group " Mollusca," in a class 

 " Vermes." 



Lamarck separated the parasitic worms, for which he retained 

 the term " Vermes," as a class distinct from the Chaetopodous 

 worms, to which he gave the name " Annelides." Lamarck's 

 "Vermes" is thus essentially synonymous with the "Entozoa' r 

 of various subsequent writers. And in spite of the fact that 

 as long ago as 1850 Grube 1 pointed out the affinities of the 

 Annelids with the Arthropoda, and insisted upon the unnatural 

 character of " Vermes " as a group, and although Lankester 2 was 

 one of the earliest of the more recent zoologists to give up the 

 term " Vermes," and the truth of this view has become more and 

 more evident in recent years, yet many writers still retain this 

 name almost in the sense of Linnaeus. Leuckart 3 in 1848 broke 

 up the " entozoic worms," and associated the Cestodes with the 

 Acanthocephala as " anenterous worms," which he separated from 

 the " apodous worms " (Turbellarians, Trematodes, and Leeches) ; 

 while the other parasitic forms (Nematodes) were recognised a& 

 distinct from these and placed with the Annelids. Later on, 

 however, he 4 put the Cestodes in a more natural position, in a 

 group " Platodes," which included the Trematodes, Turbellaria, 

 Nemertines, and Leeches. 



But Vogt 5 had already recognised in 1851 the affinity of these 

 various worms and invented the term Platydmia for the group, in 

 the sense in which it is usually understood at the present time. 

 The name was modified by Gegenbaur 6 to Platyelminthes, and 

 adopted by Carus, Schneider, Haeckel, and others ; Haeckel in 

 1877 removed the Xemertines from the Platyelminthes (to which 

 group, however, he gave the name " Acoelomi ") and placed them 

 with the rest of the " Vermes " as " Coelomati." Lankester 7 

 modified Vogt's terminology and still retained in his " Platyhelmia " 

 the Nemertina and Hirudinea. But recent researches on the 

 anatomy and development of the latter class, and amongst others, 

 Biirger's work on the Nemertines, have shown conclusively the 

 necessity of removing them from the neighbourhood of the Flukes, 



1 Grube, Die Fam. d. Anneliden, Arch. f. Naturgesch. 16. 1850, p. 249. 



2 Lankester, Notes on Embryology and Classification, 1877. 



3 Leuckart, Ub. Morphol. u. Verwandsch. d. Wirbellose Thiere, 1848. 



4 Leuckart, Arch.f. Naturgesch. Jahrg. 20. 1854. 



6 Vogt, Zoolog. Briefe, 1851, vol. i. p. 185. 



Gegeubaur, Die Grundzuge d. Zoologie, 1859. 



7 Lankester, The Advancement of Science, 1890 ; and Encyd. Brit. ix. edit., art, 

 "Zoology." 



