226 BESSIE NOYES 



deposits on the average one egg the first day, three the second, 

 five the third, seven the fourth, three the fifth, one the sixth, 

 and death occurs on the seventh day of maturity. 



The organism is cyhndrical, soft, slender, and worm-hke, with 

 an undeveloped foot and small toes; the eye is small, red, and 

 located on one side of the brain. The color varies from white in 

 young specimens to dark brown in mature forms near the close 

 of the life-cycle. Movement through the water is rapid for the 

 first two or three days of the life-period, but gradually the size 

 of the organism increases, a substance of a dark brown color is 

 deposited within the body, and movement becomes increasingly 

 sluggish. As ordinaril}'- found, the animals are all females and 

 reproduction is entirely by parthenogenesis. 



Thus the creature furnishes us a hardy animal, readily culti- 

 vated in small compass, passing through the cycle of birth, 

 infancy, maturity, old age, and natural death within eight days, 

 and yielding within that time a large number of progeny, pro- 

 duced without that admixture of germ cells from diverse parents 

 which so greatly complicates the problems of heredity and varia- 

 tion in most organisms. It has in these respects the advantages 

 of an infusorian reproducing vegetatively, with the important 

 diversity that here we have opportunity to study uniparental 

 inheritance through germ cells. 



The present paper gives an account of the normal life-cycle, 

 with appropriate vital statistics; an experimental and observa- 

 tional study of the question as to the appearance of the male sex 

 and fertilization; a study of variation and the results of selec- 

 tion during parthenogenesis, and an account of attempts to alter 

 the hereditary characteristics through the action of environmental 

 agents. 



All the organisms studied have descended from one individual 

 isolated by Dr. H. S. Jennings during the first week in February, 

 1919, with the exception of five 'wild' specimens which were 

 later found and cultivated for the sake of comparison. 



Proales will live and reproduce in cultures containing decaying 

 vegetable material, in hay infusion, in solutions of pasteurized 

 milk, and other similar media, but in the present work it was 



