RF.GEN ERATION I 3 7 



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 effected a mechani- 

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

 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 //£?;;//-blastula became completed to form an entire one. 

 In some of these hemi-blastulas development proceeded still 

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

 tive cavity of the gastmla, so that eventually a rudimentary 

 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 EcJiinus viicro-tiiber- 

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

 entire as regards its shape ; and that a partial forviation, 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 : — 'II 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 tliat they 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. Other than 

 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. 



