296 



THiE WONDfiR OF LIFE 



by the Radiolarian, and are able to build up carbon- 

 compounds, such as starch. They give off oxygen, 

 which is of course profitable for the animal, and they 

 doubtless utiUze nitrogenous waste products made by 



the animal. If 

 things are not going 

 well, it is always 

 open to the Eadio- 

 larian to digest its 

 partners ! The huge 

 numbers of Eadio- 

 larians — alike of in- 

 dividuals and of 

 specie s — seem to 

 indicate that the 

 symbiosis is very 

 profitable. 



The symbiotic 

 Algse are known as 

 Zooxanthellse, and 

 their occurrence has 

 been recorded in a 

 variety of animals. 

 In the Planarian 

 worm Convoluta, 



FiQ. 50. — The Green Hydra, expanded and 

 contracted. The expanded form shows 

 the male organs or testes as swellings 

 near the base of the tentacles and the 

 ovary as a swelling near the attached 

 base. The transparent ectoderm is 



seen as a layer surrounding the endoderm thev are verv abun- 

 which contains the green elements, . . 



usually regarded as symbiotic Algae. dant and quite in- 

 dispensable. Prof. 

 Keeble has shown that the larvae do not develop unless 

 they are infected, and that an adult which has been 

 driven by straitened circumstances to absorb its partners 

 can be re-infected and given a new lease of life. 



