74 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



tion varies in different Coelenterates. In a number of 

 species, the symbionts do not enter the egg. In such cases, 

 the later larval stages become infected from the surrounding 

 water. In the hydroids, it has been observed by a number 

 of investigators that the algal symbionts are carried from 

 one generation to another within the ovum. Hamann ('82) 

 studied egg formation in Hydra viridis and observed the 

 algal symbionts transferred to the egg. He believed that 

 there was no active movement of the algae into the eggs, 

 but that they were carried passively in the '^food stream" 

 from the entoderm to the egg in the formation of the yolk. 

 Such an interpretation, it appears to me, is a rather super- 

 ficial one. The experiments of Hadzi ('06) on the influence 

 of light on egg infection are interesting and significant. 

 Hydra viridis was kept in the dark during ova formation. 

 The ova developed under these conditions, but more slowly 

 and they were colorless. Out of twenty eggs produced in 

 this manner, only one developed into a polyp. This polyp 

 was also colorless, and hved but a short time. He also 

 tested the influence of colored fight on egg development. 

 In red fight the eggs developed into normal polyps, and 

 contained the algal s^mbiont. In blue and violet fight a 

 few individuals developed into polyps, while in weak green 

 fight no development was observed. 



Beijerinck ('04) discovered a free fiving alga that was 

 strikingly similar to Brandt's zoochlorellae (symbionts). 

 He inoculated some of these algae into a colorless Stentor 

 polymorphus. Vacuoles formed around the algae, and in 

 a short time they disappeared apparently as a result of 

 digestion. Experiments of a similar nature have been 

 made by various investigators with identical results. 

 These experiments indicate that there is a distinct ''speci- 

 ficity" of the organisms concerned in symbiosis. They 

 also indicate the presence of chemical or unseen differences 

 in organisms with similar morphology. 



