A. EARLAND ON RADIOLARIA. 275 



the inqiiiline xanthellee with shelter and protection as well as 

 with carbon dioxide for nutriment, while the vegetable cells yield 

 their host oxygen for respiration, and after their death the starch 

 and protoplasm which they have formed, for nutriment. This 

 symbiosis has been compared with the commensal life of the 

 Lichens, in which algoid gonidia, organisms with a vegetable 

 metastasis, and fungoid hyphse, organisms with an animal 

 metastasis, are conjoined for mutual advantage. But the com- 

 parison can be pushed too far, for while in the Lichens this 

 symbiosis is essential for the development of the organism, in 

 the Kadiolaria it has more the appearance of an adventitious 

 association. The xanthellse vary so much in number, even in 

 the same species, that they cannot be essential to its existence, 

 and in a great many species they have never been seen. Again, 

 many Radiolaria, notably the Phaeodaria, live only at consider- 

 able depths in absolute darkness ; and in these the xanthella?, 

 even if present, could not give off oxygen owing to the absence of 

 light. Still it is possible that the phaeodellae of the Ph?eodaria 

 (usually green, olive, or brown in colour), which are true cells, 

 are vegetable symbiontes which, in the absence of sunlight, are able 

 to evolve oxygen under the influence of the phosphorescence of 

 abyssal animals. 



The xanthellse are usually spherical or elliptical, sometimes 

 discoidal. They occur in varying numbers in the extra-capsular 

 bodies of many Radiolaria of the first and third legions, the 

 Spumellaria and the Nassellaria, most abundantly in the sub- 

 legion Collodaria. They have been proved to contain starch or 

 an amyloid substance. Their envelope contains cellulose, and 

 their characteristic yellow colour is due to pigment grains of a 

 similar nature to the colouring matter of diatoms. They multiply 

 by fission within the cell membrane, each cell giving origin to 

 four, which then escape. They are also capable of assuming an 

 encysted and also an amceboid condition. They may be distinct 

 forms of Algae, but possibly are only swarm -spores of larger Algae, 

 especially Fucaceae. The size of the extra-capsular xanthellae is 

 usually between '008 mm. and '012 mm. 



While the xanthellae of the first and third legions are confined 

 to the extra-capsulum, in the second legion, the Acantharia, they 

 are never found except in the central capsule. Their number 

 is variable, but rarely exceeds thirty, and they lie as a rule close 



