Regeneration . 159 



Claude Bernard and Vitzou had shown that the 

 period of growth and moulting of the higher Crustacea 

 is accompanied by a heaping up of glycogen in the liver 

 and subdermal connective tissue. Smith' found that 

 during the period between two moultings, when there is 

 no growth, the storage cells are seen to be filled with 

 large and numerous fat globules instead of with glyco- 

 gen. He also found that in the Cladocera ''the period 

 of active growth is accompanied by glycogen — as 

 opposed to fat — metabolism. ' ' He observed, moreover, 

 that if Cladocera are crowded at a low temperature the 

 fat metabolism (with inhibition to growth) is favoured, 

 while at high temperatures and with no crowding of 

 individuals the glycogen metabolism is favoured. In 

 the latter case a purely parthenogenetic mode of propa- 

 gation is observed, while in the former sexual reproduc- 

 tion takes place. The effect of crowding of individuals 

 is possibly due to products of excretion, which then act 

 on growth and reproduction indirectly by changing the 

 ''glycogen metabolism" to "fat metaboHsm." 



All these cases agree in this, that apparently specific 

 substances induce or favour growth, not in the whole 

 body, but in special parts of the body. Sachs suggested 

 that there must be in each organism as many specific 

 organ-forming substances as there are organs in the 

 body. 



We will now show that the assumption of the exist- 



» Smith, Geoffrey, Proc. Roy. Soc, B. 1915, Ixxxviii., 418. 



