UNITIES OF LIFE 



uality is very difficult to answer. Thus, fifty years ago, 

 we came to recognize floating animal-stems in the re- 

 markable siphonophora, or social medusc'c, which had 

 hitherto been regarded as individual animals, or medusa; 

 with a multiplicity of organs; further study proved that 

 each of these apparent organs is really a modified me- 

 dusa, and the whole united structure a stem. This 

 example throws a good deal of light on the important 

 question of association and division of labor. The whole 

 floating siphonophoron is, physiologically considered (in 

 respect of its vital activity), a harmoniously organized 

 animal with a number of different organs ; but from the 

 morphological point of view (in respect of form and 

 structure) each dependent organ is really an indepen- 

 dent medusa. 



It is clear, from these few illustrations, that the ques- 

 tion of organic individuality is by no means so simple 

 as it seems at first sight, and that it receives different 

 answers according as we look at the form and structure 

 (morphologically) or the vital and psychic activity 

 (physiologically). We must, therefore, distinguish at 

 once between morphological (niorphonta) and physio- 

 logical (bionta) individuals. The tree and the siphono- 

 phoron are bionta, or individuals of the highest order, 

 made up of a number of similar branches or persons, 

 the social morphonta. But, when we further dissect 

 the latter anatomically into their various organs, and 

 these again into their microscopic elements, the cells, 

 each branch or person seems to be a bion, and their 

 ^cells to be morphonta. Each multicellular organism 

 1 is, however, developed in the beginning from a single 

 cell, the stem-cell (cytula) or fertilized ovum; this is at 

 once a morphon and a bion, a simple individual both 

 morphologically and physiologically. The whole proc- 

 ess of its development into a multicellular organism con- 

 sists in a repeated cleavage of the stem-cell, the resultant 



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