GERM CELLS OF COELENTERATES 23 



for the theory supposes the germ cells to be scattered over the 

 whole body in great numbers. Clearly, there is no evidence that 

 regeneration in Coelenterates, nor in other animals, is a process 

 dependent upon the presence of germ cells. And there is abun- 

 dant evidence that the specialized cells undergo regressive 

 changes, produce masses of cells or syncytia of embryonic charac- 

 ter, and then, by differentiation and specialization form new parts 

 to replace those lost. It is, of course, equally well known that not 

 all tissues can undergo such changes or even regenerate their own 

 kind of tissue to any great extent; but this offers no evidence of 

 a correlation between regeneration and the presence of germ cells. 

 It only shows that specialization may proceed to such a degree 

 that further changes, whether progressive or regressive, are 

 impossible. 



So far from regeneration presenting evidence in favor of the 

 germ-plasm theory, practically all the experiments and obser- 

 vations show direct contradictions to this explanation. The 

 germ-plasm theory is not only inadequate to explain regenera- 

 tion, but it is shown to be incorrect, so far as this process is 

 concerned. 



d. Dissociated cells. The tissues of sponges have been broken 

 up by teasing and forcing through fine screens, and the behavior 

 of the isolated cells followed by Wilson ('07). Such cells showed 

 amoeboid activities and fused into masses which later regenerated 

 to form normal sponges. The amoebocytes first began to unite 

 to form syncytia, but collar-cells and other specialized cells also 

 took part in the formation of the masses, first passing through a 

 regressive differentiation. Mtiller ('11) largely confirmed Wilson, 

 but believes such specialized elements as collar-cells do not assist 

 in the regeneration. Fresh-water sponges also undergo normal 

 degeneration phenomena by a de-differentiation of cells to produce 

 embryonic masses which later produce new organisms. This 

 latter process is qiiite distinct from gemmation. 



Later, Wilson ('11) extended his experiments to hydroids. 

 Here also the isolated cells fused into syncytial masses which 

 secreted perisarc about themselves, then formed ectoderm and 

 entoderm layers, and later regenerated hydranths, complete and 



