1 88 



REGENERA TION 



tion exists can only be determined by such an experiment. If two 

 fused organisms result from the fusion of two eggs, it would show 

 the structure of the egg is of such a kind that two organizations can- 

 not readjust themselves into a single one of double size. Moreover, it 

 is important to discover whether any difference exists as to the stage 

 of development at which the union is brought about, for it is conceiv- 

 able that while a rearrangement is possible at one stage, it might 

 not be at another. 



B 



FIG. 56. A. Tadpole to show where the V-shaped piece is cut from the tail. B. Later stage of 

 same with a new tail-like outgrowth from the anterior end of tail. 



It has been shown that two blastulae of the sea-urchin can be 

 united to form a single embryo. I found ('95) that occasionally two 

 blastulae stick together and fuse, so that a single sphere of double 

 size is formed. As a rule two gastrulae and two more or less com- 

 plete embryos develop from each double blastula, but in a few cases 

 I found that a single embryo may be formed, that shows, however, 

 traces of its double origin. Driesch has more recently (1900) suc- 

 ceeded l in bringing about more readily a union of two segmenting 



1 Eggs without membranes were placed in sea water without calcium, to which a few 

 drops of sodium hydroxide have been added. 



