No. 559] NOTES AND LITERATURE 



437 



with diverse environmental history give more fertile pairs; pos- 

 sibly conjugation involves regularly the death of a large pro- 

 portion of the gametes. 



Here perhaps belongs also the study by Woodruff (14) show- 

 ing that Paramecium caudatum and Paramecium aurelia are 

 distinct species: 



Since one of the crucial tests of a species is its ability to breed true 

 to type indefinitely, aurelia and caudatum have adequately met this 

 test during more generations than any other animal under observation 

 (14, page 237). 



2. External Factors. — Studies of the effects of a long list of 

 external factors on reproduction have branched out from the 

 main trunk given by the study of the life cycle. In his ''seed 

 paper" of 1905 (1 ). "Woodruff had included a number of experi- 

 ments with various chemical and physical agents, showing par- 

 ticularly that Protozoa are extremely sensitive to solutions of 

 electrolytes. He followed this up in 1908 (4) with a study of 

 the effects of alcohol. This showed that : 



(1) Minute doses of alcohol will decrease the rate of division at one 

 period of the life cycle and increase it at another period of the life 



Woodruff and Bunzel (8) further undertook a precise study 

 of the directly destructive effects of various salts and acids on 

 Paramecia taken from the pedigree culture serving for the 

 trunk experiments. The results of this work, not bearing directly 

 on reproduction, lie a little to one side of the main stream of 

 experimentation ; the conclusion is : 



Considered as a whole, the results of the experiments indicate a 



toward Paramecium and the ionic potential of the ions employed 1 3. 

 page 194). 



A considerable number of studies (11, 12. 17, 18, 19, 20, 21) 

 are devoted to analysis of the effects of the environmental con- 

 ditions to which the animals are subjected in their natural lives, 

 —the culture media — upon reproduction and vitality. A paper 

 by Woodruff (12) on "The Effect of Excretion Products of 

 Paramecium on its Rate of Reproduction" concludes: 



