240 University of California Publications in Zoology [VOL. 19 



From the above similar and repeated observations I was forced to 

 conclude that we haveJhere a case of parasitism or possible symbiosis. 

 Such a Collodictyon seldom engulfed food and seemed well nourished, 

 as though by holophytic nutrition. For some months, in spite of daily 

 observations, I never observed pseudopodia protruded from the sulcal 

 region in such individuals, which condition is characteristic of the 

 holozoic phase. If such be regarded as parasitism, Collodictyon must 

 be regarded as the parasite, and Cklorella must provide the nourish- 

 ment. Possibly it had best be regarded as a case of benign domestica- 

 tion, the by-products alone being used. To be truly a symbiotic relation- 

 ship, Chlorella would have to be benefited, and I have not been able 

 to determine that this was the case. I do know that it thrived fully as 

 well, if not better, outside the organism. 



The question of inclusions functioning in a parasitic or symbiotic 

 relation, is not a new one. The "yellow cells" of Radiolaria is one of 

 the most interesting as well as most disputed points, and one which is 

 still far from being satisfactorily solved. They were first described 

 by Huxley in Thalassicolla, and verified by Johannes Miiller and 

 Haeckel. Cienkowski (1871) strongly contended that they were para- 

 sitic algae. The discussion progressed with Richard Hertwig (1898, 

 1902), K. Brandt (1881, 1882, 1885), Entz (1882), and F. Keeble 

 (1909), adhering with certain reservations or modifications to Cien- 

 kowski 's interpretation. Miiller had at first indicated the possibility 

 that they were phases in the life cycle, but later gave up this concep- 

 tion. In 1909 Moroff and Stiasny contended that the yellow cells of 

 Acanthrometron pellucidum were part of the developmental cycle ; in 

 1910 Stiasny extended this interpretation to Sphaerozoa and Radio- 

 laria generally. Such a view was not accepted without reservation by 

 Minchin (1912) ; so the question stands, awaiting further and decisive 

 evidence. 



In Collodictyon, there can be no doubt that the inclusions are algae. 

 They correspond with the free Chlorella of the aquarium. I did at 

 first mistake them in observations upon unstained material to be ele- 

 ments of multiple fission, but was forced to give this up upon critical 

 examination. Neither can it be a situation similar to Euglena gracilis 

 (Zumstein, 1899), in which the typical chloroplast is lost and an 

 Astasia-like phase results; though such evidence furnishes a most 

 interesting possible analogy. That an ultimate lichenoid condition 

 might result is a possibility and from such a relation Collodictyon 

 might be transformed from a holozoic to an independent holophytic 

 state. 



