42 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



they taper posteriorly, sometimes very gradually, ending in a spine- 

 like tip. Their nuclei are much smaller than those of P. caudata lata 

 and are resting in a much earlier phase of mitosis. The two pear- 

 shaped nuclei are united by a thread and each is seen to be in an 

 anaphase condition. 



Fig. 19. — Protoopalina caudata, mostly form attenuata, from Bombina bombina ; 6, 



e, AND i ARE ENTERING ON DIVISION ; a TO e, MAGNIFIED 460 DIAMETERS/ f TO i, MAGNI- 

 FIED 117 DIAMETERS. THE ANTERIOR ENDS ARE ABOVE EXCEPT IN g. 



INTERMEDIATE FORMS. 



Strange as it seems, at first glance, to include the two forms just 

 described in the one species caudata^ they so completely intergrade 

 that there seems no alternative. Reference to the accompanying 

 figures makes this evident. In figure 19, a and rf, are seen individ- 

 uals from Bonibina homMna which are almost typical attenuata. In 



