SEFrEMBER 9, 1910] 



SCIENCE 



347 



-upon the parthenogenetic female as to cause 

 her to produce sexual daughter females. 

 These chemical compounds may not be final 

 products of decomposition, but break up into 

 or form other products which possess different 

 properties. When these compounds are form- 

 ing, a higher temperature under certain con- 

 ditions augments them and consequently they 

 appear in greater abundance suddenly, and 

 thus act upon the parthenogenetic females and 

 cause male epidemics in the third generation. 



As the culture water becomes older the de- 

 composition rapidly decreases and the special 

 chemical compound which causes sexual 

 females appears in inappreciable quantities, if 

 at all, throughout the liquid. However, in the 

 bottom of old culture jars decomposition may 

 not have ceased, as was evident in the breaking 

 up of the parthenogenetic pedigree strain into 

 sexual females at the end of twenty-six 

 generations. This chemical substance is evi- 

 dently something which appears more or less 

 abundantly at first in decomposition and then 

 later disappears or its influence is counter- 

 acted by other substances. 



Whether the production of parthenogenetic 

 females is sometimes brought about by the 

 action of a different chemical compound or 

 sometimes by the mere absence of the sexual 

 female producing chemical compound is not as 

 yet altogether clear, but the latter possibility 

 seems more probable. 



On January 16, 1910, I began feeding two 

 pedigree strains of rotifers with the small 

 flagellates, Polyfoma, which grew in a culture 

 of about one hundred grams of fresh horse 

 manure and flve hundred cubic centimeters of 

 tap water, that had been steam sterilize..' for 

 about one hour. The Polytoma grew very 

 quickly in these eiiltures and in 24-48 

 hours immense numbers of them were pro- 

 duced. These new food cultures of Poly- 

 toma ranging from 24-96 hours old were 

 diluted, one part culture water to two parts 

 tap water, and used to grow the rotifers 

 in. Such diluted Polytoma cultures, none of 

 which were over 96 hours old and in which 

 the culture water was cooked, have been used 

 from January 16 to August 13. In each gen- 



eration of these two strains ten daughter 

 females were isolated from one to three 

 mothers. Each individual was placed in a 

 separate watch glass and kept at room tem- 

 perature. In these two strains of a hundred 

 generations and consisting of one thousand 

 individuals in each strain no sexual females 

 have ever appeared during a period of about 

 seven months. 



These long parallel series of parthenogenetic 

 females are similar to Punnett's pure female 

 strains. However, the parthenogenetic females 

 of both strains in the generations between the 

 ninetieth and the one hundredth, have pro- 

 duced sexual daughter females when placed in 

 very little dilute culture solution and fed upon 

 the green flagellate, Clilamydomonas, thus 

 showing that these are not pure parthenoge- 

 netic female strains, and that the production 

 of sexual females has been suppressed since 

 January by some condition of the culture 

 water. 



These results are similar to those obtained 

 by Shull who used old culture water, although 

 produced by using newly made cooked culture 

 water and extending over a longer period of 

 time. At the end of some starvation experi- 

 ments in which Shull used dilute culture 

 water, he makes this general concluding state- 

 ment, " The larger proportion of sexual forms 

 in the starved families is not due to lack of 

 food, but to the absence of chemicals which, in 

 the well-fed families, prevent the appearance 

 of the sexual forms." 



In February, 1910, I had in the laboratory 

 some pure cultures of a colorless flagellate, 

 which seemed to be a species of Peranema. 

 These flagellates were very resistant and could 

 live and swim about normally several hours in 

 distilled water, and were readily eaten by the 

 rotifers. These flagellates were taken in quan- 

 tities, put into large test-tubes, placed on a 

 large electric centrifuging machine, and col- 

 lected in the bottom of the tubes by centri- 

 fugal force. The old culture water was re- 

 moved, clean tap water added, and the con- 

 tents thoroughly mixed. Then it was centri- 

 fuged again and the protozoa collected at the 

 end of the tubes. This process was repeated 



