20 SYMBIOGENES1S 



There is, however, an important proviso to be borne in 

 mind before it can be assumed that Convoluta presents a case 

 of genuine or progressive biological symbiosis. 



When referring to the abstemious habit of C. roscoffensis we were 

 careful to state that it is the mature animal which does not take up 

 solid food. As a matter of fact, from the time of hatching to the 

 period of maturity, C. roscoffensis feeds, and feeds voraciously. Indeed, 

 its catholicity of taste is remarkable. Diatoms, unicellular algse, spores 

 of various kinds, and, in the absence of more nutritious substances, 

 grains of sand are swallowed with avidity. Arrived at maturity, it 

 ceases to ingest solid food-substances. As old age comes on, it begins 

 to feed upon its green cells. Groups of such cells in all stages of 

 digestion, and varying in colour from yellowish-green to brown, may be 

 seen lying in large vacuoles in the central digestive tissue of the bodies 

 of old specimens of C. roscoffensis. Thus, though, as we shall see 

 presently, the green cells of C. roscoffensis play an all-important part 

 in the economy of that organism, they are not the sole purveyors of 

 nourishment to it. Throughout a considerable part of its life, 

 C. roscoffensis is able to help itself to the solid food supplied by the 

 microflora and fauna of its environment. 



Unlike C. roscoffensis, its ally, C. paradoxa, knows no abstemious 

 fits. Throughout its life it is a glutton. 



The abstemiousness of C. roscoffensis is thus seen to be 

 only temporary, a fact which reflects rather unfavourably on 

 the claim of symbiosis, or, at any rate, renders it necessary to 

 qualify the term. Nevertheless, the fact that this abstemious- 

 ness, so long as it lasts, is based on the efficiency of Convoluta' s 

 own "garden" of green cells in providing supplies is 

 significant enough. 



Prof. P. Geddes has demonstrated that the green cells of 

 C. roscoffensis are capable of photosynthesis, and their green 

 pigment is spectroscopically identical with the chlorophyll of 

 green plants. 



That the products of the photosynthetic activity of the 

 coloured cells are available for the nutrition of the animals 

 which contain them has also been demonstrated. Prof. Keeble 

 suggests that the appearance of yellow-brown cells in 

 C. paradoxa recalls, in this respect, that of cells of a mammary 

 gland in its active stage. This analogy is interesting and 



