506 S. O. MAST 



amounts to the solutions in which the organisms live. Under 

 such conditions it is, of course, impossible to say precisely what 

 the chemical constitution is and how it is affected by the addition 

 of chemicals. For example, most fresh waters are distinctly 

 alkaline. When acid is added to such a solution it is evident 

 that it can affect organisms as acid only after, the alkalis are 

 neutralized. Addition of acids may, therefore, merely subject 

 the organisms to an increase in salts and a decrease in alkalinity. 

 The importance of this will become evident as we proceed in our 

 discussion. 



MATERIAL AND METHODS 



Spondylomorum is a colonial organism consisting of sixteen 

 zooids. It is ellipsoidal in form, about .05 mm. long and .035 mm. 

 wide. Each zooid contains among other structures a prominent 

 eye-spot and two flagella, considerably longer than the colony. 

 The colonies are fairly active. They are definitely postero-ante- 

 riorly differentiated and always swim with the anterior end or 

 surface ahead, rotating continuously on the longitudinal axis. 

 They respond definitely to light and orient fairly precisely, being 

 positive under certain conditions and negative under others. 



Spondylomorum is not very common. It is usually found in 

 stagnant pools rich in decaying organic matter. In October, 

 1912, it was found in great abundance by my colleague, Prof. 

 E. A. Andrews, in a small puddle near a well frequented by ducks 

 and chickens. I am greatly indebted to him for supplying me 

 with numerous collections of this material. In the laboratory I 

 succeeded for several months in raising the colonies in hsiy infu- 

 sion, and in some cultures they became very abundant, but in 

 January they all died out. I had intended to continue the work 

 on these forms and delayed pubHcation, hoping to obtain more 

 laboratory cultures, but in this I have been unsuccessful. 



Two methods were used in ascertaining the effect of different 

 chemicals on the sense of orientation in light: 1) Numerous 

 colonies were put into about 1 cc. of solution from the culture 

 jar or pure distilled water in a square watch-glass. This was then 

 placed at a given distance from a window and left until the col- 



