September 9, 1910] 



SCIENCE 



345 



the production of new characteristics by over- 

 feeding and the fixation of these characters. 

 The time during which these experiments 

 have been in progress has been divided into 

 three periods. Daring the first period, which 

 includes the time immediately following the 

 starting of the culture, the form of the head 

 varied very widely under the new food con- 

 ditions, but it soon returned to the original 

 form when original conditions were restored. 

 In three to four months after the culture was 

 started, the form of the head was more regu- 

 lar and there were fewer aberrant individuals. 

 Young females returned more slowly to the 

 original head form when changed to original 

 environment. The third period began almost 

 two years after the culture was started and it 

 was found that the young no longer returned 

 to the original helmet form when original 

 conditions were restored. A larger helmet 

 persisted, thus showing a tendency toward 

 the fixation of a new helmet form. 



All of these experiments are still in progress 

 and a more extended report on the results is 

 promised at some future date. 



C. Jdday 



Madison, Wis. 



in the Devonian of Missouri," by C. Schuch- 

 ert ; " George Frederic Barker." 



SCIEyTIFIG JOURNALS AND ARTICLES 

 The American Journal of Science for Sep- 

 tember contains the following articles : " Use 

 of the Grating in Interferometry," by C. 

 Barus ; " Fox Hills Sandstone and Lance 

 Formation (' Ceratops Beds ') in South Da- 

 kota, North Dakota and Eastern Wyoming," 

 by T. W. Stanton ; " New Occurrence of Hy- 

 drogiobertite," by E. C. Wells ; " New Occur- 

 rence of Plumbojarosite," by W. F. Hille- 

 brand and F. E. Wright; " Heat of Forination 

 of the Oxides of Cobalt and Nickel," and sixth 

 paper on the " Heat of Combination of Acidio 

 Oxides with Sodium Oxide," by W. G. Mixter; 

 " Mosesite, a New Mercury Mineral from Ter- 

 lingua, Texas," by F. A. Canfield, W. F. Hille- 

 brand and W. T. Schaller ; " Eesearehes upon 

 the Complexity of Tellurium," by W. E. Flint ; 

 " Gravimetric Estimation of Vanadium as 

 Silver Vanadate," by P. E. Browning and H. 

 E. Palmer; " Braehiopod Genus Sijringothyris 



SPECIAL ARTICLES 



THE INFLUENCE OF EXTERNAL CONDITIONS UPON 

 THE LIFE CYCLE OP HYDATINA SENTA 



The search for the factors which regulate 

 the production of the parthenogenetic and the 

 sexual phases in the life history of the rotifer, 

 Hydatina senta, has been conducted for some 

 time. Maupas concluded that temperature 

 regulated these two phases, while Nussbaum 

 found that the controlling factor was food. 

 Punnett and the writer' were unable to eon- 

 firm these results. Eecently Shull" has claimed 

 that the absence of certain chemicals in the 

 culture water causes the sexual phase to be 

 produced, while the presence of these chemi- 

 cals prevents the appearance of the sexual 

 phase. This suggestion is probably partially 

 true, but it does not seem to express the whole 

 truth, nor solve satisfactorily the whole 

 problem. 



During the past two years I have kept pedi- 

 gree strains or families of these rotifers con- 

 tinually in the laboratory and have made some 

 observations which may lead to a clearer 

 understanding of the conditions which control 

 the production of the sexual and partheno- 

 genetic phases in the life cycle of this rotifer. 



A general food culture for rotifers is 

 usually made by adding about one hundred 

 and fifty grams of fresh horse manure to 

 about two thousand cubic centimeters of ordi- 

 nary water and allowing this mixture to stand 

 at room temperature after being inoculated 

 with a miscellaneous lot of microorganisms. 

 It is readily noticeable that in large jars of 

 such newly made food cultures in which roti- 

 fers have been placed, that sexual females 

 (females capable of producing either males 

 from small parthenogenetic eggs or females 

 from large fertilized eggs) appear quite abun- 

 dantly for a few days or weeks, then gradually 

 disappear and only parthenogenetic females 

 remain in the cultures as they become older. 



In June, 1909, several general cultures 



' Journ. Exp. Zool., Vol. 5, pp. 1-23. 



'Amer. Nat., Vol. 44, pp. 146-150. 



