and Laboratory Methods. 1139 



the diameters being taken as zero, and those in the semicircles to the right and 

 to the left of this zero being numbered in corresponding series till they met at 

 180°." The dish containing the animal was placed over this circle in such a 

 way as to bring the center of the animal over the center of the circle, and its 

 head directed towards the zero point on the circumference. The apparatus was 

 set up in a dark chamber in order to exclude extraneous light, and the illumina- 

 tion for the experiment was obtained from a Welsbach burner placed at a con- 

 stant distance from the center of the circle. The heat rays were absorbed by an 

 alum solution contained in a parallel-sided glass vessel, which was placed between 

 the light and the dish containing the animal. The light. was made to enter 

 horizontally only, or, by the use of a screen and reflector, vertically from above. 

 The anterior end of the animal and zero point of the circle were towards the 

 source of light entering horizontally in one set of experiments, and away from it 

 in another set, while in a third the light entered from above. For one series the 

 eyes were removed by cutting off the head with a sharp scalpel. In each experi- 

 ment the animal was observed from the time it left the center till it crossed the 

 circumference of the circle. Its path was marked free-hand on a circle which 

 was a duplicate of the one on the black board, and later measured in millimeters. 

 The angle on the circumference at which the animal crossed was read directly, 

 and the time taken in the passage from center to circumference was obtained by 

 means of a stop-watch. 



This method, with modifications to suit particular cases, will undoubtedly 

 prove very valuable in work in phototaxis. Exact records can be obtained of the 

 angle of deviation in the path caused by light coming from one direction ; of the 

 form of the path taken and the distance travelled ; and of the rate of travel under 

 constant light stimulation. The principal result of the investigation was to show 

 that planarians, with or without eyes, when moving horizontally totuards a source 

 of light are more deflected from an ideal course (to zero on the scale) than when 

 moving under a vertical light, and conversely, when moving horizontally away 

 from a source of light they keep nearer to an ideal course. The animals without 

 eyes are affected by light in the same way as those with eyes, but their reaction 

 is less precise. The rate of movement of the decapitated animals is slower than 

 that of the normal. The reactions are believed to be due to a dermatoptic 

 function. R- ^^ 



Matthews, A. P. Some Ways of Causing Mi- Several new methods are given in addi- 



totic Division in Unfertilized Arbacia Eegs. . ^ ^i u- u u i j u^^^ 



Amer. Jour. Physiol. 4: 343-347, 1900. ^lon to those which have already been 



described for producing cell division in 

 the sea urchin egg. Lack of oxygen is first discussed. Unfertilized Arbacia 

 eggs were placed in an Engelmann gas chamber in sea water, and hydrogen gas, 

 carefully freed from acid, was passed through the preparation. After twenty to 

 thirty minutes' exposure to the hydrogen, oxygen was admitted for ten minutes, 

 and then again hydrogen was allowed to act for twenty minutes. The eggs 

 were then transferred to fresh sea water, and in a comparatively short time clear 

 areas appeared in the cytoplasm, and division into from two to eight cells took 

 place. Continuous exposure to hydrogen kills the eggs before any segmentation 

 occurs. Eggs which have been too long exposed immediately liquify completely 



