214 University of California Publications in Zoology [Vol. 19 



depression. Here then is a structure which by location and analogy 

 may be correlated, or at least compared, with the highly specialized 

 gullet of forms like Euglena. 



There is a tendency at times for Collodictyon to become exceedingly 

 eccentric in its form (pi. 8, figs. 9-18). Its irregularity is for the 

 most part accompanied by a flattening and warping, the sulcus cleav- 

 ing one of the narrow margins, making a secondary if not, indeed, a 

 fundamental bilateral symmetry. On occasions when such irregu- 

 larities were prevalent, I have tested the culture, trying to determine 

 if possible a cause for such variation. The water of the aquarium was 

 neutral or only slightly alkaline, by litmus paper and litmus solution 

 tests. Alkalinity tended to produce rounded, globular, conical, or pear- 

 shaped forms, the sulcus itself being reduced to a minimum. Con- 

 centration tests were not accurate, but in my judgment I could detect 

 no variation upon this. Death always resulted when the density 

 was such as might be judged sufficient to rupture such a fragile 

 organism. That oxygen content plays an important part in the vari- 

 ation in shape there can be no doubt. Sufficient or excessive oxygen 

 supply tends to produce well rounded forms, a deficient supply, flat- 

 tened, eccentric forms. This test was easily made by having a sub- 

 strate of filamentous and unicellular algae, which in the sunshine kept 

 the aquarium filled with bubbles of oxygen. The alternative inter- 

 pretation that light and heat caused the rounding up, was tested by 

 placing the aquarium without any algae in the sunlight. The forms 

 then retained their original shapes. The chemical content so far as 

 organic salts in solution is concerned was probably not variable enough 

 to produce the variations, tests having been made for sodium, calcium, 

 and magnesium salts with negative results. By adding carbon dioxide 

 slowly in small quantities similar eccentricities of shape resulted as 

 from deficient oxygen. From these tests I concluded that variation of 

 shape was largely a question of respiration, irregularities being either 

 degenerative stages or adaptations to meet deficient oxygen supply. 

 Carbon dioxide in excessive amounts would be immediately converted 

 into carbonic acid gas and thus make the culture slightly acid. This 

 is in accord with the acidity tests. 



In observing moribund forms disintegrate (text fig. C, 1-12), all 

 food vacuoles were seen to be extruded, the body flattened, and patho- 

 logical vacuoles, largely water, became apparent in the sulcal axis. 

 These ruptured leaving the body very irregular in shape. Successive 

 formation of these vacuoles finally caused complete disintegration of 



