274 LIGHT AND THE BEHAVIOR OF ORGANISMS 



warm water from which they were taken soon resumed their 

 positive reaction." 



Change in temperature does not however cause reversal 

 in reactions to Hght in all organisms. Strasburger (p. 608) 

 discovered that while the swarm-spores of Ulothrix, Ulva 

 lactua, Chaetomorpha aerea, and Chytridium vorax respond 

 much like those of haematococcus, those of Scystosiphon 

 lomentarium, Chilomonas curvata, Botrydium and Bryop- 

 sis could not be induced to reverse by changing the tem- 

 perature; and the same is true for the copepod Labidocera, 

 and for Daphnia pulex and Cypris, according to the work 

 of Parker (1902, p. 117) and Yerkes (1900, p. 417). I have 

 observed the same in a number of organisms referred to 

 below. It must be admitted that the above statement with 

 reference to the copepods is somewhat too broad, since 

 Parker tested the reactions only in 10°, 30°, and 35°, and 

 Yerkes studied only the effect of increase in temperature 

 above the normal. 



Original observations. — Observations on the effect of 

 changes in temperature on reactions to light in microscopic 

 forms were made by mounting them on a Pfeffer warming- 

 stage under a large cover-glass sealed and supported by 

 means of a ring of vaseline. The Pfeffer warming-stage 

 consists of a glass cell 1X6X8 cm. with three holes in the 

 ends, one for a thermometer, the other two for water inlet 

 and outlet. It is fastened on the stage of a compound 

 microscope and admits of observation under either low or 

 high power. The temperature is regulated by passing hot 

 or cold water through the openings, and recorded by means 

 of the thermometer. It was thus possible to subject the 

 organisms to gradual or sudden changes in temperature 

 ranging from a little above zero to nearly 100°. 



May II, 1908, at 9 a.m. a few drops of solution were 

 taken from some collected the preceding day and mounted 

 on the warming-stage. The solution contained numerous 

 specimens of Euglena viridis, Euglena deses, Phacus trique- 

 ter, and a few specimens of Euglena spiragyra and Phacus 



