160 Plant Animals: a Study in Symbiosis [May 15, 



WEEKLY EVENING MEETING, 



Friday, May 15, 1914. 



Dr. Doxald Hood, C.Y.O. M.D. F.R.C.S., Vice-President, 

 in the Chair. 



Professor Frederick Keeble, M.A. D.Sc. F.R.S. 

 Plant Animals: a Study in Symbiosis. 



The discourse treated of the bionomics of Convoluta roscoffensis and 

 0. faradoxa, two marine TurbeUarian worms, the bodies of which 

 contain algal cells. 



The relation between worm and alga is intimate — indeed, in- 

 fection by the alga is a condition for the development of the 

 animals. 



The mode of infection of the body of larval C. roscoffejisis has 

 been followed in detail, and is described in memoirs contributed to 

 the ' Quarterly Journal of Microscopic Science.' * 



The infecting organ of G. roscoffensis — a species of Chlamy- 

 domoiias — is a unicellular motile green alga. It is swallowed by the 

 just hatched larva and transferred to vacuoles in the body, but 

 instead of undergoing digestion like the other organisms ingested 

 by voracious larval G. roscoffensis, the alga multiplies by division 

 and forms a green assimilatory tissue beneath the skin of the animal. 

 With the dev'elopment of this tissue the animal ceases to ingest solid 

 food, and relies entirely on the algal cells for supplies of carbo- 

 liydrate and of protein. The green cells of the body of C. roscoffensis 

 lose the power of independent existence, and each generation of 

 G. roscoffensis is infected anew by free-living green cells. 



The waste nitrogenous substances produced during the meta- 

 l)olism of the animal serve as the raw materials from which the 

 <rreen algEe of the body of G. roscoffensis manufacture amino- 

 compounds and proteins, which substances serve for the nutrition 

 of both animal and alga. 



The discourse dealt also with the various phenomena of periodicity 

 exhibited by the plant-animals, and showed how these phenomena 

 enable the convolutas to maintain their several stations on the sea 



shore, t 



[P. K.] 



* See also the volume entitled Plant Animals (Cambridge Manuals of 

 Science), 

 t Op. cit. 



