Maech 12, 1909] 



SCIENCE 



425 



" Wild " cultures of Paramecium were found to 

 consist of many diverse races, which remain con- 

 stant in relative mean size when propagated in 

 "pure lines," by fission. Eight such differing 

 " pure lines " were isolated and propagated side 

 by side under the same conditions for many 

 months. The smallest race had a mean length 

 below 100 microns; the largest a mean length 

 above 200 microns. Most existing races fall into 

 two groups: (1) those with mean length above 

 170 microns; (2) those with mean below 140 

 microns. The former group corresponds to what 

 has been described as the species eaudatum, the 

 latter to aurelia. A single race falling half-way 

 between the two groups was found; such races are 

 rare. 



Within the pure race there is much variation 

 due to environmental conditions and to growth, 

 but such variations are not inherited. Large and 

 small individuals of the same race produce prog- 

 eny of the same mean size, so that the character- 

 istics of the progeny depend on the fundamental 

 constitution of the race, not on the individual 

 peculiarities of the parent. It is not possible to 

 produce by long continued selection diverse races 

 from a single race. 



The diverse races retain their relative sizes 

 throughout the life cycle, including conjugation. 

 Owing to the assortative mating described by 

 Pearl, there is a tendency for the diverse races to 

 remain isolated even when conjugation occurs. 

 The Reactions of Didinium nasutum with Special 

 Reference to the Feeding Habits and the Fvmc- 

 tions of Triohocysts : S. 0. Mast, Woman's Col- 

 lege of Baltimore. 

 Light Reactions in Euglena and Stentor coeruleus: 



S. 0. Mast, Woman's College of Baltimore. 

 Notes on Opalina: Matnaed M. Metcai.f, Oberlin 

 College. 



A paper describing the phenomena to which 

 these notes refer will appear in the Archiv f. 

 Protistenkunde, Bd. XIII., Heft 3. 

 The Measurement of Relative Toxicity and of 

 Differences of Physiological State ly the Use 

 of Protozoa: A. W. Petebs, University of Illi- 

 nois. 

 Selection of Food in Stentor ccsruleus: Asa A. 

 ScHAEFFEK, Johns Hopkins University. 

 From a capillary pipette, potato starch grains, 

 particles of sand, bits of dSbris, Euglena viridis, 

 Phacus triqueter, Trachelomonas volvocina, etc., 

 were fed in mixed order, on to the disk of a 

 Stentor. The path and fate of each particle was 

 recorded. The starch, sand and dSbris were al- 



most invariably rejected, while the organisms, 

 either freshly killed or living, were invariably 

 ingested. When the Stentor became more and 

 more filled up, more and more of the organisms 

 were rejected, until eventually all organisms, a; 

 well as all starch, sand, etc., were rejected. 



In some experiments it was shown that some 

 organisms are eaten while others are not; thus in 

 a stream of Euglena viridis and Trachelomonas 

 volvocina, fed in mixed order, although both kinds 

 of organisms were eaten at the beginning of the 

 experiment, the Stentor ate only Euglena in the 

 latter part of the experiment, rejecting all 

 Trachelomonas and also some Euglena. 



Thus Stentor can " select " food particles from 

 a stream containing food and non-food particles. 

 Further, Stentor can " select " one kind of food 

 from a mixture of several different kinds, such as 

 Euglena from Trachelomonas, etc.; and it is 

 highly probable that Stentor, when nearly replete, 

 " selects " certain individuals to the exclusion of 

 others, of the same species. 



Selection can be explained upon purely objective 

 grounds as determined by the action of the 

 stimulus in the particle upon the ingesting 

 mechanism (including the varying physiologic 

 state) of Stentor. 

 Duration of the Cycle of Paramecium: Lobande 



Loss WooDEUFF, Yale University. 



A culture of Paramecium has been carried on a 

 varied culture medium for twenty months, during 

 which time 930 generations have been attained. 

 Conjugation has been prevented by the daily isola- 

 tion of individuals, and no artificial stimulation 

 has been employed. " Abnormal " physiological 

 or morphological changes have not appeared in 

 the specimens. 

 Effects of Centrifugal Force on the Organization 



and Development of the Eggs of Ascidians and 



Mollusks: E. G. Conklin, Princeton University. 

 The Organization of the Egg of a Medusa: E. G. 



CoNKLiN, Princeton University. 



The Oogenesis of Gumingia telUnoides (Conrad) : 

 H. E. JoBDAN, University of Virginia. 

 The primary oocyte at the beginning of the 

 growth period has a nucleus of three microns 

 diameter. The nuclear reticulum is achromatic 

 except for a large eccentric nucleolus. At slightly 

 later stages chromatic masses appear in the nu- 

 cleus and are generally arranged in pairs. Such 

 pairs probably represent presynoptic bivalent 

 chromosomes. The arrangement of the chromo- 

 somes indicates parasynapsis. Still later in the 



