240 \VM. A. KEENER AND A. L. PICKENS. 



surface and when it swims. This reversal of polarity has been 

 overlooked by the earlier observers of Trichodina Steinii. Kent 

 (81) implies that Trichodina pediculus (Ehr.) has the usual 

 polarity. Fulton (1923) in making a thorough review of the 

 literature of this genus and in his own observations, seems not 

 to have encountered this reversal of physiological and morpho- 

 logical polarity. This author, as well as earlier investigators, 

 has also overlooked the homologies that we have draw r n between 

 this ectozoic peritrich and Vorticella. 



This animal should, therefore, serve as the basis of some 

 interesting work done upon its physiological axial gradient. 

 From what we have seen of its morphology we expect to find 

 that its axial gradients have been reversed in their sequence; 

 for it is seen that there has been a morphological reversal, 

 despite the homologies that we have indicated. In Vorticella 

 there is an emphasis placed upon the anterior region in that the 

 loop of the meganucleus and the micronucleus lie in that region. 

 In Trichodina Steinii the morphological emphasis is reversed; 

 for in this form the loop of the meganucleus and the micronucleus 

 lie in the posterior region of the cell. 



Thus it appears that in Trichodina rather complex adaptive 

 structures are but the homologues of simpler structures found in 

 Vorticella; but that correlated with the ectozoic mode of living 

 Trichodina has undergone a reversal of polarity that involves 

 both its physiological axis and its nuclear complex. 



LITERATURE. 

 Agassiz, L. 



'50 Remarks on the Little Bodies seen on Hydra, which have been Described 



as Parasites. Proc. Bost. Soc. Nat. Hist., Vol. 3, p. 354. 

 Claparede, Ed., and Johannes Lachmann. 



'58 Etudes sur les Infusoires et les Rhizopodes. (Extrait des tomes V, VI, et 



VII des " Memoires de 1'Institut Genevois.") 

 Faure-Fremiet, Emmanuel. 



'05 La Structure de 1'appareil fixateur chez les Vorticellidae. Arch. Protisten- 



kunde. Bd. 6, p. 207. 

 Fulton, John F. 



'23 Trichodina pediculus and a New Closely Related Species. Proc. Boston 



Soc. of Nat. History, Vol. 37, pp. 29. 



Jennings, H. S. 



'04 Contributions to the Study of the " Behavior of the Lower Organisms." 



Carnegie Institution, Washington, D. C. 

 Kent, W. Saville. 



'81 Manual of the Infusoria. London. 



