II. ONTOGENY 349 



2. The Mechanism of Regeneration 



Organisms can regenerate in general their lost parts, and some- 

 times even the whole individual is formed from a small piece. This 

 regeneration process is particularly conspicuous in plants, although 

 some animals such as sponges and hydroids can regenerate new indi- 

 viduals from cuttings, as do many plants, but in many animal species 

 the restoration of lost parts is more limited. 



It is a note-worthy fact that, in the case of organisms able to re- 

 generate, sectioning of a structure is followed by a brief period in 

 which the "blastema" forms, undifferentiated cells accumulating in the 

 region of the wound (19). Thus, it appears that certain cells in the 

 region of the wound are reduced in their structure to the primitive, 

 undifferentiated, from which subsequently the complicated, differ- 

 entiated structure is anew recovered. Regeneration must be, there- 

 fore, a reversible structural change of protoplasm just as ontogeny. 



Anaerobic glycolysis is the metabolic process peculiar to undiffer- 

 entiated, primitive cells and was discovered by Warburg in cancerous 

 and in embryonic tissues. It shoud be noted that this primitive meta- 

 bolic process was found in normal cells after injuries, indicating the 

 occurrence of functional reduction in the wound regions which must 

 be based upon the structural reduction (20). 



Such a reduction of the structure to a primitive state may be 

 caused by the stimulus of injury, and in each cut piece a primitive 

 structure like that of germ cells may be produced, from which the 

 original, differentiated structure will subsequently be restored, if each 

 piece has the capacity to form a normal adult. 



The remarkable process of reassociation of cells after dissociation 

 occurs in some sponges and hydroids. For example, pieces of Micro- 

 ciona prolifera, the common red sponge of the Atlantic coast, can be 

 squeezed through silk bolting cloth so that the cells are separated or 

 dissociated. If these fragments are allowed to settle upon the bottom 

 of a dish of sea water and remain undisturbed, they will become reas- 

 sociated in small spherical masses within 24 hours and then develop 

 as thin encristations upon the bottom (21). Attention should be paid 

 to the fact that masses arising first are of a larval stage similar to 

 the typical normal larva. This phenomenon may be also based on the 

 formation of primitive structures by cutting. 



Thus there is no doubt that somatic cells of certain organisms can 

 recover their primitive structure when they are stimulated by such a 

 simple factor as cutting. Germinal cells may develop into somatic. 



