206 University of California Publications in Zoology [Voi . 19 



5-6) would naturally lead one to suspect a somatella stage, though this 

 variation may be accomplished by reduction through successive binary 

 fissions. 



In culture experiments I have tried malted milk (one-sixteenth of 

 one per cent solution and varying strengths), crushed Myriophyllum, 

 boiled mushroom solution, amoeba agar, sterilized soil with tap water 

 boiled thirty-five minutes, beef extracts, and quince-seed jelly as sug- 

 gested by Turner (1917) for Euglena. Most of these were partially 

 successful, but only temporarily so, Collodictyon soon disappearing 

 from the culture. 



Among associated forms in the aquarium, I have found : Pandorina, 

 Peridinium, Euglena, Amoeba of the Umax group and others, Platy- 

 dorina, Gonium, Actinoplirys, Bodo, Chlamydomonas, Chilomonas, 

 Coleps, Stylonychia, Euplotes patella and E. charon, Microthorax, and 

 Colpidium; rotifers (Branchionus, Philodina, and Chaetonotus} ; 

 Ulothrix, Oscillatoria, Chlorella, Tetraspora, Spongomonas, Lager- 

 heimia, Scenedesmus, Pediastrum, Selenastrum, Coleochaete, Navicula, 

 Closterium, Cosmarium, and several undetermined desmids and 

 diatoms. 



I have considered the possibility that the life history of Collodictyon 

 may in some way be related to its association with goldfish. Aside 

 from the balancing of the plant and animal life of the aquarium, I 

 have looked for some symbiotic or parasitic relationship, but have 

 found none, other than the fact that I have been unable to keep a 

 permanent culture in other than a goldfish aquarium. I tried a fairly 

 well balanced stickleback aquarium without success. In aquaria where 

 there were abundant Ulothrix and other algae, Collodictyon did not 

 persist. The voracious habits of this animal led me to believe that it 

 is not symbiotically dependent upon goldfish, nor has it any other 

 method of food-taking involving absorption; but its habits of engulf- 

 ing free living protozoa and algae may wed it to a well balanced con- 

 dition such as would be found in a satisfactory goldfish aquarium. 

 There is a bare possibility that the life-history is dependent upon the 

 presence of living fish, though Carter and France's observations are 

 opposed to such an interpretation. In examination of stomach and 

 intestinal contents I found no evidence of symbiosis or parasitism 

 relating the two. Examination of the gills and body for ectoparasites 

 never failed to yield some of these forms. This was probably due, 

 however, to their abundance in the water. 



It is rather a prevalent custom to use cover-glass preparations in 



