2()() lULLETIX 120, I'NITED STATES NATIONAL .MUSEUJM. 



I . madaf/ascariensis (fig. 114, p. 150). Another series includes the 

 species CepecUa (jJobosa (fig. 119, p. 154), Opallna helenae (fig. 188, 

 p. i^lG), O. helenuc flujUomedume (fig. 189, p.. 217), and 0. moreletel 

 (fig. 190, p. 218). One Avould not for a moment urge that these two 

 series show the actual derivation of Opalinas from Cepedeas, but they 

 show the existence even to-day of more than one set of intermediate 

 forms and this argues that possibly the flattening by Avhich the 

 Opalinas were derived from the Cepedeas may have taken place more 

 than once. Ofalina viryula may l)e a flattened Cepccha. It is unique 

 in the character of its endospherules, and its occurrence in India in- 

 stead of in North America, which is the home of the narrow Opalinas, 

 suggests that it nuiy have arisen independently of the other Opallnae 

 augiistae. 



In this connection we should note again (see p. 175) that twice 

 at least in the family Opalinidae cylindrical forms have given rise 

 to flattened, forms, for ZeUericlJa doubtless evolved from Protoo- 

 palina, and Opcdina doubtless evolved from Cepedea. 



The genus Pvotoopcdina does not grade into the genus Zelleriella 

 through any series of species as yet studied, unless it be through P. 

 ovoidea (fig. 38, p. 67) and P. xyster (fig. 3^, p. 68), of which the 

 former is considei-ably flattened and the latter still more flattened, 

 especially in front, l)ut there are no species of ZeUcrieJJa that seem to 

 complete the series. 



The genus Pi^otoopaHna does grade into the genus Cepedea^ so far 

 as the number of the nuclei are concerned. P. quadnnucleata has 

 four distinct nuclei, yet from its nuclear character it is clearly a 

 Protoopalhm. Prootoopcdina axonucleata may have eight, or gven 

 more, nuclei, but although these are rather small, they still seem 

 to be ProtoopaUna nuclei rather than Cepedea nuclei. Xot only the 

 general appearance of the nuclei, but also the small number of 

 macrochromosomes (4) is Profoupalina-Wke. Cepedea lanceolata 

 (fig. 102, p. 137), as described by Bezzenberger, has but four nuclei, 

 occasionally five, but its nuclei show the characteristic Opallna con- 

 dition, Avith reticulate chromatin net, and large chromatin masses 

 beneath the nuclear membrane. I do not think we have to-day any 

 species which are known to form a true intergrading series of related 

 forms between the genera ProtoopaUna and Cepedea^ but the probable 

 manner in which the Cepedeas arose from the Protoopalinas does 

 seem to be indicated by the series P. formosae (fig. 50, p. 81 ) , P. 

 .quadrinucleata (fig. 51, p. 82), P. axomicJeata (fig. 52, p. 83), and 

 Cepedea lanceolata (fig. 102, p. 137). 



In describing the several species of Protoopalina we followed a 

 general order indicated by gradual progress from the uninucleated 

 to the multinucleated condition. I would not claim that the species 

 thus placed in juxtaposition are in everr case near relatives. In 



