268 Bl'LLKTIX 120, UNITED STATES NATIONAL MUSECM. 



tlio niicroclu'oniatin fihrillao, <% the aclironiatic alveolar luicleo- 

 plasin; 9, the absence of amitotic division of any of the nuclei, 

 such as is seen in the pinching apart of the macroniiclens in 

 Euciliates; 10. the persistent orientation of the two nuclei in the 

 binucleated genera. A pleurinucleate condition, generally confined 

 to a more or less restricted phase of the life cycle, is not rare among 

 the Plasmodroma, and we know a number of species of Euciliata 

 which at times assume a multinucleated condition. Some are usually 

 multinucleated. The Euciliata, in general, however, are definitely 

 hi nucleate, but so are Arcella, Olardhi., and some other Plasmodroma. 

 The numerical conditions in the nuclei are less distinctive than the 

 structure and functions of the nuclei. The Opalinidae show no 

 approach to nuclear differentiation into a large, trophic nucleus and 

 a small, reproductive nucleus. In this regard they are far removed 

 from the Euciliata. Their possession of distinct sets of trophic 

 chromosomes and reproductive chromosomes, and the absorption of 

 the former before sexual union, parallels physiologically the pres- 

 ence and behavior of trophic nucleus and generative nucleus in tho 

 Euciliata. It seems a condition somewhat similar to that which we 

 know among the Plasmodroma, for many species of Plasmodroma 

 have two distinct sets of chromosomes, one derived from the nuclear 

 chi'omocentrosome and the other from the peripheral layer of the 

 nucleus, but we have not satisfactory data as to the behavior of these 

 two groups of chromosomes in connection with sexual phenomena. 

 The Opalinidae ai'e markedly different from and less specialized than 

 the Euciliata in the structure of their two nuclei and their behavior 

 at about the time of sexual union. 



The manner of af<e.rnaJ rrprodiutlon deserves some emphasis. The 

 Opalinidae reproduce by longitudinal and by transverse fission. The 

 Flagellata have for the most part only longitudinal fission, with the 

 exception of Platyinonas (unpublished observations l\v I. F. 

 Lewis -^), Prashiodadus {''Eicglenopsis,''' Davis, 189-1), SaJpingoeca 

 gracilis (Kent, 1881-1882), Salpingoeca pohjgonntum (Penard, 

 1921), Eiiglena (?), and some few other forms among the gi-een 

 flagellates (Algae?), mostly less clearly described. The Euciliata 

 reproduce by transverse fission, except perhaps among the Peritricha, 

 and it is usual to interpret the fission in the Peritricha as in the same 

 morphological plane, for it runs transverse to that surface of the 

 body which bears the cytostome. The Opalinidae show regularly 

 both the Flagellate and Euciliate types of fission. 



The prcsexual phenomena in Plasmodromes and Euciliates are 

 probably fundamentally similai-. Reduction occurs in eadi, the full 

 chromosome number being restored by fertilization. The Euciliata, 

 apparently because of their unique nuclear conditions, are peculiar in 

 the presexual and postsexual nuclear divisions and the nuclear meta- 



** Noted here with his? permission. 



