REGENERATION 



137 



perfect, but only organs of slight importance were wanting in 

 them. Chabry himself has drawn no theoretical conclusions 

 from his observations ; Driesch,* however, has made certain 

 deductions from a series of similar experiments on the eggs of 

 Sea-urchins. By continued shaking, Driesch etfected a mechani- 

 cal separation of the two first segmentation-cells, and obsened 

 that at first each of them continued to undergo further segmen- 

 tation just as would occur in the entire egg, but that later on the 

 resulting //t7;//-blastula became completed to form an entire one. 

 In some of these hemi-blastulae development proceeded still 

 further, the invagination taking place to form the primary diges- 

 tive cavity of the gastnila, so that eventually a rudimentarv 

 pluteus-larva — -which, though small, was in other respects nor- 

 mal — could be recognised. 



Driesch sums up his results in the following words : — ' These 

 experiments therefore show that under certain circumstances 

 each of the two first segmentation-cells of Echinus micro-tuber- 

 culatus can give rise to a larva of the normal form, which is 

 entire as regards its shape; and that a partial formation, and 

 not a semi-formation, occurs in this case.' The author con- 

 cludes that his results ' fundamentally disprove the existence of 

 special regions in the germ which give rise to special organs.' 

 and adopts the following view stated by Hallez f : — '11 n'est pas 

 des lors permis de croire que chaque sphere de segmentation doit 

 occuper une place et jouer un role, qui lui sont assignes a Tavance.' 



Although I am far from wishing to assert that we are at 

 present in a position to give a perfectly reliable and detailed 

 explanation of the extremely interesting and important results 

 of the experiments just described, I nevertheless cannot help 

 thinking that thev do not in the least necessitate the giving 

 up of the view which entails a predestination of the individual 

 segmentation-cells, and, in fact, of cells in general. Qlloer- thaji 

 experimental methods may lead us to fundamental views^_and an 

 experiment may not always be the safest guide, although it may 

 at first appear perfectly conclusive. Even Driesch himself 

 doubts whether the above-mentioned experiments made by 

 Roux are really conclusive, though, in my opinion, he is wrong 



* H. Driesch, ' Entwicklungsmechanische Studien, Zeitschrift f. wiss. 

 Zoologie,' Bd. 53, 1891. 



t Hallez, ' Recherches sur rembryologie des Nematodes," Paris, 1885. 



