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PROCEEDINGS OF THE NATIONAL, MUSEUM 



VOL. 87 



THE GENUS PROTOOPALINA 



In this genus the several species are fairly distinct, more so than 

 in any other genus of Opalinidae. This is in agreement with its 

 archaic character, there having been time for gradual divergence to 

 well-demarcated species. The archaic character of Protoopalina is 

 indicated: (1) By its agreement in morphology with the first stages 

 in development of each of the other three genera, Zelleriella, Cepedea, 

 and Opalina; (2) by its wide geographical distribution, Euro-Asia 

 (except southern India and the islands supposed to have been once 



'^^. 





Figure 127.— Geographic distribution of Protoopalina. 



parts of the Indian Ocean continent ''Lemuria"), Africa, Malaysia, 

 Australasia, South America, Central America and the Antilles, North 

 America (except the northeastern portion) (fig. 127); (3) by the com- 

 parative morphology of the four genera, Protoopalina being less 

 developed in structure and showing in its series of species how the 

 other genera might readily have been derived from it; (4) by the 

 agreement of the comparative morphological series, Protoopalina, 

 Cepedea, Opaiina, with the course of the larval development of the 

 higher genera, complete and convincing evidence of phylogeny (Met- 

 calf, 1923a); (5) by the resemblance of a group of Protoopalinae of 

 southern, almost sub-Antarctic distribution (subgeneric group I) to 

 the mother ceUs of the male gametes in Protoopalina, Cepedea, and 

 Opalina, the only genera the sexual phases of whose development have 

 been studied, and the similar character of the zygotes in Opalina. 

 These elongated forms with slender tails, which are naked near the 

 tip, are strikingly alike and seem to be archaic in character. I have 

 regarded the tailed species in Protoopalina as constituting the most 



