MICROSYMBIOSIS 73 



present in the ectoderm in some species. In some cases 

 there appears to be a definite locaHzation of the symbionts 

 in a particular part of a tissue. Thus, in the canals of the 

 so-called liver of the Portuguese man-of-war the algal 

 symbionts are only present in the upper cells of the canals. 

 These cells do not have the typical entoderm-cell appear- 

 ance, while those in the lower haK of the canals suggest 

 secretory and absorptive functions. The symbionts are 

 also found in other parts of this animal. When the animal 

 reproduces by budding, the daughter forms receive the 

 algal symbionts in a passive manner. The number of 

 symbionts present in a cell varies considerably in different 

 species. The usual number is four to eight, but in some 

 cases it runs up into the hundreds. 



An idea of the intimacy of the relation between the 

 algae and the host in some instances is suggested by the 

 ease with which the former can be eliminated when the host 

 is kept for a time in a dilute solution of glycerine. Gly- 

 cerine is known to be highly toxic to many bacteria and 

 other low forms of hfe with a notable exception of certain 

 filterable viruses whereas it has little or no effect upon 

 higher forms. It is supposed that this effect is produced 

 largely through its influence upon osmotic pressure within 

 the cell. 



The distribution of the symbionts in a hexacoral {Adamsia 

 diaphana) described by K. C. Schneider ('02) is also in- 

 teresting and indicative of the specificity of certain cells 

 to the symbiont. The symbionts are found in special 

 cells in the septa which produce a bulging at that point. 

 These special cells have a morphology which differs from 

 that of the other cells of the septum. This appears to be 

 the lowhest animal in which there has been found to be a 

 distinct morphologic response in the host to the presence 

 of the symbiont. 



The behavior of the algal symbionts in sexual reproduc- 



