1 70 "Journal of Comparative Neurology and Psychology. 



for those containing fertilized eggs. I found, as stated above, that 

 specimens which contain large daughter-colonies or spores deflect 

 to the right more, in moving horizontally across the aquarium, than 

 do those containing small daughter-colonies; and also that the 

 former move to the right along the wall of the aquarium nearest the 

 source of light, more definitely than the latter. Oltmanns may 

 have been misled in his conclusions by some such reactions. The 

 effect of such reactions on the place of aggregation of Volvox 

 colonies is strikingly brought out in the following observations: 

 After bringing specimens of Volvox to the laboratory, they were 

 usually put into 4 liter battery jars, which were exposed to the 

 light from a 16 candle power electric bulb placed at any desired 

 distance from the jars. Under such conditions it was frequently 

 noticed that the major portions of the colonies aggregated in a 

 region some little distance to the right of the point in the jar 

 directly opposite the bulb. At first this was thought to be due to 

 reflection from the table or wall and other objects about, but after 

 all such reflection was eliminated this reaction was still found to 

 take place. It was also found that if the colonies were put into 

 the plate glass aquarium and exposed to light from a Nernst glower 

 situated so that the rays entered the aquarium at right angles to 

 the side, many more collected along the side nearest the source 

 of light, to the right of the middle than to the left, being most 

 numerous but a short distance from the end of the aquarium.^ 

 The specimens to the right of the middle of the aquarium, in every 

 instance, were nearly all large and contained well developed daugh- 

 ter-colonies or spores, while those to the left were nearly all small. 

 The difference in size between those to the right and those to the 

 left could be clearly seen with the naked eye, but they also showed 

 a marked difference in reaction. Colonies taken from the right 

 edge of an aggregation in a battery jar, July 26, 1905, deflected 

 on an average 8° to the right in swimming horizontally toward a 

 source of light, while the average deflection of others taken from 

 the same jar near the left edge of the aggregation was 15° to the 

 left. This accounts, in part at least, for the collection of the 

 smaller colonies to the left and the larger ones to the right, but 

 the chief reason why the larger ones are found to aggregate to 

 the right is because they turn to the right, after coming in cou- 

 sin all these experiments especial precautions were taken to eliminate reflection and refraction. 



