THE OPALINID CILIATE INFUSORIANS. 



B}^ Maynard M, Metcalf. 



Of the Orchard Laboratory, Oberlin, Ohio. 



^ 1. INTRODUCTION. 



This paper Avas completed for publication April 20, 1921. During 

 the years 1906 to 1908 the author was engaged in studies of the Eu- 

 ropean species of Opalinidae, investigating the structure of the 

 known European species and following the life history of Profoo- 

 palina [^^ Opalina^''] hitestinalis and of P. caudata. Observations 

 were also made of the sexual and presexual phases of the life-cj^cle in 

 Opalina ranarum and Cepedea [" Opalina "] dimidiata. The results 

 of these studies were published in four papers.^ Previous to these 

 studies the work of others, especially Engelmann (1875 and 1876), 

 Zeller (1877), Bezzenberger (1904), and Leger and Duboscq (1904, h) 

 had given us a good idea of the general character of twelve species 

 of the family {caudata^ coracoidea^ dimidiata.^ intestinalis^ lanceo- 

 Jata^ lata, Tonga, vmcronucleata, obtrigona, ranarum, saturnalis, 

 and ^^zellerV'Y^ and Neresheimcr (1906, 1907) had published the re- 

 sults of his studies of the life-histories of Cepedea [" Opalina "] 

 dimidiata, and Opalina ranarum. Stokes (1888) " Opalina flava '^ 

 can not be identified from his description. Additional species have 

 since been described as follows : 



Opalina virgula, by Dobell (1910), 



Protoopalina [^^ Opalina^''] hinuclcata, hy Raff (1911), 



Protoopalina ['■^ Opalina''^] hylamm, by Raff (1911). 



Protoopalina' \;'-Opalina''^\ m^Yoz^/ca, by Metcalf (1912), 



Protoopalina [^^Opaliiia^^] tenuis, hy Raff (1912), 



Protoopalina [^^Opalina^^] dorsalls, by Raff (1912). 



Protoopalina [^^ Opalina''''] acuta, by Raff (1912), 



Opalina cincta, by Collin (1913), 



Protoopalina [^^Opalina^^] p)rimordialis, by Awerinzew (1913). 



Zelleriella [''Opalina'''] aiitilliensi^, hy MetcAli (1914), 



Zelleriella {"■Opalina^'''] hrasiliensis, hy Pinto (1918), and 



> See the Literature List, Metcalf, 1907, a; 1907, b ; 1907, c ; 1909. 



"This "species" is treated in the present paper as a forma of Ccpcdca (Umidiafa. 



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