348 



SCIENCE 



[X. S. Vol. XXXII. No. 819 



four or five times until the protozoa were 

 thorougKly washed, and no trace of the old 

 culture water remained. 



Several parthenogenetic female rotifers 

 were also washed by dropping them into four 

 or five successive dishes of tap water. Then 

 series of watch glasses were prepared contain- 

 ing five cubic centimeters of distilled water 

 in which there were large numbers of the 

 Peranema, and amounts of cold culture water 

 varying from one drop to four cubic centi- 

 meters. In pure distilled water the rotifers 

 soon died and also in the dishes containing 

 very small quantities of the old culture water, 

 while in the dishes containing larger amounts 

 of the old culture water the rotifers lived and 

 reproduced normally. Under these varying 

 conditions three generations were reared, but 

 no sexual females were produced in any of the 

 dishes. 



These experiments in which the quantity of 

 old culture water varied from zero to four 

 cubic centimeters and only parthenogenetic 

 females were produced seem to indicate that 

 the substance which causes sexual females to 

 be produced was absent altogether in this old 

 culture water. If this is true, then perhaps 

 the mere absence of the substance which 

 causes the sexual females to be produced is 

 always sufiicient to cause the production of 

 parthenogenetic females and it is unnecessary 

 to look for a specific substance which causes 

 their production. 



Newly made uncooked cultures of horse 

 manure and water in which rotifers can live 

 readily are more or less dilute, but as they 

 grow older they become more concentrated by 

 the end products of decomposition. If mere 

 dilution of substances in the culture water, as 

 ShuU seems to maintain, produces sexual 

 females, then epidemics of males ought to 

 occur in culture water during the very first 

 days when such culture water is most dilute, 

 and not several days later as it becomes more 

 concentrated by the end products of decom- 

 position. However, the epidemics of males 

 that occurred in my two general culture jars 

 which were between two and three weeks old 

 were preceded by a production of males which 



did not exceed thirty per cent, during a period 

 of at least a week. 



In some pedigree families of rotifers that I 

 observed in 1907 and 1908, it was found that 

 in any single family of forty to fifty daugh- 

 ters, if there were any sexual daughters they 

 occurred among the first half of the family. 

 When a mother was isolated she was fed and 

 then remained in the same food culture water 

 without the least change until all of her 

 daughters were produced. Sometimes she 

 would produce ten or more sexual daughters 

 in succession, which were often preceded by 

 several parthenogenetic sisters and always fol- 

 lowed by parthenogenetic sisters. 



It is plain that dilution of the culture water 

 did not occur to cause these series of sexual 

 daughters and it is conceiveable that the 

 chemical substance that produces males, in 

 some cases, when sexual females occurred 

 among the first daughters, was present in the 

 culture water at the time of isolation of the 

 mother, and in other cases, when the sexual 

 females appeared between the tenth and 

 twenty-fifth daughter, this substance was 

 formed some time after the mother was iso- 

 lated and had laid some of her eggs. In all 

 cases its influence disappeared as the culture 

 became older and no sexual daughters ap- 

 peared in the last half of the family. 



It seems evident from all the observations 

 that some culture waters totally lack the power 

 to cause sexual females to be produced, others 

 lack this power at first, but acquire it later, 

 while still others possess it as the cooked new 

 cultures and some old cultures, but are unable 

 to use it unless the culture water is diluted. 



In a summary I would maintain that there 

 seems to be a definite, but transitory, chemical 

 substance produced in appreciable quantities 

 in the decomposition processes in newly made 

 horse manure cultures that can so act upon 

 the parthenogenetic females as to cause them 

 to produce sexual daughter females. When 

 this substance is absent no sexual females are 

 ever produced, but only parthenogenetic 

 females are produced, and when this substance 

 is present in culture water which is too con- 

 centrated its influence is counteracted and no 



