No. 634] SHORTER ARTICLES AND DISCUSSION 



157 



environment and the behavior of the macronucleus and that the 

 macronucleus assumes different shapes and appearances under 

 different cultural conditions. 



Is this amicronucleate Paramecium able to exist indefinitely 

 without conjugation involving a micronucleus and without re- 

 organization of nuclear material, or is there another type of reor- 

 ganization in this race? A nuclear reorganization, if present, 

 must evidently be of a different type from that described by 

 Erdmann and Woodruff. 



These and similar problems are interesting, not only in them- 

 selves, but because Paramecium has been studied in great detail 

 by Jennings and others with reference to the occurrence of cyto- 

 plasmic variations. The amicronucleate race, however, is impor- 

 tant because the variation is one of nuclear structure. The 

 importance and interest of the study is increased by the fact 

 that the micronucleus is usually considered to be an aggregation 

 of generative or hereditary chromatin and the body which sup- 

 posedly initiates reproductive processes of all types and from 

 which, in sexual reproduction, the new nuclei are formed. 



Eugene M. Landis 



Zoological Laboratory, > 



1. Dawson, J. A. 1919. An Experimental Study of an Amicronucleate 



Oxytricha. 1. Study of Normal Animal with an Account of Canni- 

 balism. Jour. Exp. Zool, Vol. 29, No. 3. 



2. Hance, R. T. 1917. Studies on a Race of Paramoecium Possessing Ex- 



tra Contractile Vacuoles. 1. An Account of the Morphology, Physiol- 

 ogy, Genetics and Cytology of this New Race. Jour. Exp. Zool, 

 Vol. 23. 



3. Calkins, G. N. and Cull, S. W. 1907. Conjugation of Paramecium 



aurelia (caudatum). Arch f. Protistenkunde, Bd. X. 



4. Erdmann, R. and Woodruff, L. L. 1916. Periodic Reorganization 



Process in Paramecium caudatum. Jour. Exp. Zool, Vol. 20. 



NOTE ON THE OCCURRENCE OF A PROBABLE SEX- 

 LINKED LETHAL FACTOR IN MAMMALS 

 The occurrence of sex-linked lethal factors in Drosophila is a 

 matter of common knowledge to most biologists. Since mammals 

 have an essentially similar type of sex determination in so far 

 as their dimorphism of sperm is concerned, it is theoretically 

 possible that sex-linked lethal factors should occur among them. 



