542 PROCEEDINGS OF THE NATIONAL MUSEUM vol.87 



OPALINA LARVAKUM Metcalf 



Figures 111, 112 



Opalinas of the larvarum type are fouiid in tadpoles of Rana clamitans 

 Latreille, R. catesbeiana Shaw, R. palustris LeConte, R. pipiens 

 Schreber, R. sylvatica LeConte, and doubtless in the tadpoles of other 

 frogs whose adults bear narrow species of Opalina. The changes in 

 the Opalinae are, however, much more extensive than the final change 

 from orbicular forms to definitely narrow Opalinae. I have followed 

 the opalinids in R. clamitans and R. catesbeiana through their life 

 history, and Miss Margaret Cowles has studied with me the life history 

 of 0. virguloidea in R. sylvatica, both tadpoles and adults. 



In a paper before the National Academy of Sciences at its meeting 

 in Washington in April 1925 (Metcalf, 1926), I reported that 0. 

 larvarum, after fertilization in the R. clamitans tadpole, started life as 

 a uninucleate form pointed behind and resembling a Protoopalina 

 with one nucleus, a condition that is found in daughter cells immedi- 

 ately after fission (fig. Ill, a). The first division of the nucleus, 

 unaccompanied by division of the body, establishes a typical Pro- 

 toopalina condition, with two nuclei (fig. Ill, c and d). Some at 

 least of these Protoopalina-like young stages have a long, naked, 

 posterior point and thus resemble adults of those species belonging to 

 what I have regarded as the most archaic subgenus of Protoopalina. 

 Nuclear division continues, occurring more often than fission, bringing 

 about multinucleation (fig. 111). For a time, up to a condition with 

 six to eight nuclei, the nuclei remain for the most part in a line along 

 the longitudinal axis of the little animal and it then resembles P. 

 axonucleata (fig. Ill, /). As the nuclei become more and more nu- 

 merous they no longer keep their axial alignment, assuming a Cepedea 

 condition (fig. Ill, g). Up to a stage with 10 or 12 nuclei their pos- 

 terior ends are generally sharp-pointed. Those with about 20 nuclei 

 are rounded behind. At an earlier or later stage of their development 

 these Cepedea-like forms begin to broaden and flatten in front, the 

 flattening gradually extending farther back until the cylindrical 

 Cepedea is transformed into a broad, orbicular, flat Opalina. Some 

 of these have as few as 8 nuclei (fig. Ill, h). Others are found in 

 which many nuclei are present when the flattening is beginning at the 

 anterior end (fig. Ill, g). In metamorphosing tadpoles with four 

 legs, and perhaps with the tail beginning to be absorbed, some of these 

 many-nucleate, very broad Opalinae become narrower and more 

 elongated, i. e., become Opalinae angustae. None of the broad, flat 

 forms have been found of very large size. The opalinids all dis- 

 appear at the time of metamorphosis, mostly before the narrow 

 form is assumed. 



