i8o Regeneration 



process of differentiation of organs and tissues, in cer- 

 tain forms at least. We have to imagine that some 

 of the cells or interstitial tissue is digested and that as 

 a consequence the organ loses its characteristic shape. 



Giard and CauUery have found that a regressive 

 metamorphosis occurs in Synascidians, and that the 

 animals hibernate in this condition. The muscles of 

 the gills of these animals are decomposed into their 

 individual cells. The result is the formation of a 

 parenchyma which consists of single cells and of 

 cell aggregates resembling a morula. ^ 



Driesch,^ experimenting on the regeneration of an 

 Ascidian, found that when he cut off the gills and 

 siphons of the animal the portion removed was able 

 to regenerate a whole animal. The gill-piece excised 

 contained no heart, no intestine, and no stolon, and all 

 these organs were regenerated from the gills. In a 

 number of cases the regeneration took place by bud 

 formation at the edge of the wound, but in other cases 

 the gills were transformed into an undifferentiated mass 

 of tissue from which the missing parts of the animals 

 arose by budding and new gills were formed. 



It is probable that the two cases are only quantita- 

 tively different. In both, autodigestion of certain cell 

 constituents and possibly of whole cells must take 

 place in order to obtain material for the formation of the 



* The writer quotes this after Driesch. 



" Driesch, H., Arch. J. Entwcklngsmech., 1902, xiv., 247, 



