THE OPALTXIli CILIATK IXFUSOIIIAXS. 269 



moiphoses. Opalinids. being but temporarily pleurinucleated and 

 liavin<r uiiiiiucleated gametes, do not show the pecidiar presexual 

 and postsexual behavior of the nuclei. 



Opalinidae differ from Euciliata in general in having male 

 (jametes which differ markedly in form as Avell as in size from the 

 female gametes. In Vorficelhie, to be sure, one sees small motile and 

 large nonmotile gametes, but tlie differences are chiefly differences of 

 •size. Neresheimer (1907) claimed that the sexual phenomena in 

 Opalinidae resemble those of Plasmodroma more than those of 

 p]uciliata. but the marked heterogamy sets the Opalinidae apart from 

 both groups. The resemblance is to Ehizopods rather than Eufla- 

 ^I'llates. It IS noteworthy in this connection that in Paramecium the 

 migrant and the stationary sexual nuclei differ in size, the more 

 active being perceptibly the smaller. 



The life cycle, as a whole, in Opalinidae is similar to that of 

 Euciliata. except, indeed, for the formation of the secondary nuclei 

 if Nereshaimer's account should be accepted. Hartmann (1910) de- 

 scribes for " Trichonympha hertwigi " presexual phenomena which 

 closely parallel Xereshaimer's description for Cepedea and Opcdlna^ 

 but Hartmann's results are so confused in some essential features that 

 the phenomena all need restudy before they can be used for compari- 

 son. As Ave know little, if anything, of sexual phases in the life- 

 histories of P^lagellata we can not make comparisons here. 



The mitotic meclidnixin in Opalinidae is peculiar in having no 

 centrosomes. Apparently the persistant attachment of eacli chromo- 

 some to both poles of the persistent nuclear membrane b}- means of 

 threads of chromatin does away with any need of centrosomes as 

 fulcra for the mitotic moAements. But other nuclei in both Euciliates 

 and Plasmodromes have persistent nuclear membranes. The struc- 

 tural phenomena and the movements in mitosis in Opalinids are 

 clear, but the manner of their derivation from conditions usual in 

 other groups is not clear.^ There seem to be no informing compari- 

 sons to be draAvn with either Euciliates or Plasmodromes. 



The occurrence of mnitotic diri^rt07i in the macronucleus of Eucili- 

 ates is not comparable to anything in Opalinids, owing doubtless to 

 the unique character of the macronucleus, and its temporary place in 

 the life e<-onomy of the organism possessing it. 



The Ghrotnidial phenomena described by Neresheimer (1907) and 

 " confirmed " by Dobell (1907) agree with descriptions of conditions 

 in such Plasmodroma as, for example. Ehizomastigina. They are 

 utterly unlike anytliing knoAvn among the Euciliata. On the basis 

 of these conditions. Neresheimer Avould entirely remove the Opa- 

 linidae from the Ciliata. But Kofoid (1921). in an address 

 before the American Society of Zoologists, has shown the in- 

 accuracy of the descriptions of the formation of nuclei from 

 chromidia in several of the most often quoted instances. Phenomena 



