70 GEORGE ALFRED BAITSELL 



the cultures is such as to show that an apparently perfect physio- 

 logical condition of the gametes at the time of conjugation is no 

 guarantee that the syzygy will be a fertile one. 



The other view, that the infertility of conjugation in animals 

 which have been under identically the same conditions of envir- 

 onment is due to to an inability to establish certain new relations, 

 is a suggestive one and harmonizes with the idea first stated by 

 Treviranus and later contended for by Weismann ('91), that the 

 real purpose of conjugation is to bring about variations in the 

 progeny. The work of Jennmgs ('11) with paramaecia in which he 

 shows that the progeny of the conjugants are more variable than 

 those of non-conjugants appears to furnish experimental proof of 

 this idea. 



Whatever be the true significance of conjugation and the cause of 

 the many infertile syzygies that have been noted not only in these ex- 

 periments but also b}'- other investigators working on other species, 

 the results here obtained show that the death of theex-conjugants 

 was not due, as far as could be told by the study of both living and 

 prepared material, to low vitality previous to conjugation or to ab- 

 normal conditions at the time of conjugation, and the evidence 

 derived from the present study points to the conclusion that one of 

 the chief factors in producing infertile syzygies is an identity of the 

 environmental history of the gametes. 



In the experiments recorded in this paper it has been shown that 

 descendants from the same original animal act differently with re- 

 gard to conjugation when kept in different media, even though 

 the other features of their environment be the same. In the stock 

 of the Sb culture kept on the beef medium conjugation occurred 

 at the 350th generation after having been kept on this medium for 

 about four months. In a sub-culture, isolated from this one at the 

 150th generation and kept on a hay infusion medium, no conjuga- 

 tion ever occurred and this culture at the time it died out had been 

 under observation altogether eleven months and had passed 

 through a total of 572 generations. Again in a sub-culture isola- 

 ted from the hay sub-culture and placed on the beef medium, con- 

 jugation occurred in the stock some three and one-half months 

 later, after the culture had passed through 120 generations on the 



