— 624 — 



competenti sperimentatori moderni nel campo della meccanica dello sviluppo. 



Pfluger observed that the position of the medium piane of the body of embryos that h e 

 developed from eggs turned into unusual positions does net, as a rule, correspond to he 

 I l first cleavage, but that the embryo generally lies on the meridian of the 

 ? ha passes thro«gh & the primary egg axis and the highest poin o the egg » * 

 position Since any meridian may happen to be placed uppermost the ernbry may 

 theJor d velop upon any one of the primary meridiana and hence the material must 

 be ot pous around the primary axis. Furthermore, since the embryo appean , alway 

 below the middle of the egg, in whatever position the egg may he, we must conclude 

 +w in eaoh meridian the material is also isotropie. 



It n ay Tpointed cut that while more recent work has substantiated, on the 

 .hole the Ltter conclusions af Pfluger (not, however, the supposed action of gravity on 

 Z ved. appresso), just stated, stili the results of studies of regenerative phe- 



L::' 0 f rganisms sbow that the conclusions are not necessarily the only ones dedu- 

 ib" f om th experiments; for, although it may be true that any possible primary in - 

 dLn of the e-g may become the median piane of the body of the embryo, it does not 

 Uow hat h r°e is no one organized piane always present in the normal egg, , e. the 

 0 II a ol b entirely isotropie. That this may be the case is shown in the regeneration 

 of piTces of adult animals in which a piece cut to one side of the old median piane may 

 d IToP a i e piane of symmetvy of its own. This possibility must be also admi ed for 

 h e7g. If we Lbstitute the term « totipotence », meaning that any meridian of *. e g 

 has tt possibility of becoming the median piane of the embryo, in place of Pfluger s 

 trm « isot P y », w, remove this element of possible error from bis statement ». 



Neiraltro libro del Morgan (Die Entrvickelung ecc., PP . 113-114) cosi sono nas- 

 «nn+p le tre più importanti conclusioni di Pfluger: 



D drei wi htigsten Schlusse, zu denen Pfluger gelangte, waren: 1. der vorausge- 

 setze Zusammenhang zwischen der Wirkung der Schwerkraft auf das Ei und seme Far- 

 eh uL 2 d ss es 1 Bezug auf die Bildung des Embryo keinen Unterschied ausmacht, 

 au hem W ge sich das & Ei teilte, und 3. das Eimaterial, da ja der Embryc , auf jedem 

 T 1 de Eies auLten kann, als isotropisch anzusehen ist. Von diesen drei Schlussen i 

 de er te falsch ... ». perchè « Roux and Born have shown that the only action tha 

 g av t hàs'on the frog's !gg is to bring about a rearrangement of 

 L a phenomenon that Pfluger has not observed. The lighter parts flow to the highest 

 eSon o the egg, and the heaviest to the bottom of the egg, hence the change ni t e 

 Son * 1 deavage planes observed by Pfluger ^that begin in 

 toplasmic P art of the egg» (Regeneration, pag. 243) . Der zweite £ 

 zutrefiend und bei alien spàteren Diskussionen iiber die Bedeutung des lurchungsp o 

 s es spielL er cine wichtige Eolie. Der dritte Schluss ist wahrscheinlich . . unzu treff d 

 a l er enth.lt ein wichtiges Stiick Wahrheit. Wenn wir stattzu behau^en <he 

 seien alle gleich, vielmehr angeben, dass sie, wenn sie auch drtTeren sind, doch poten 

 tiell fahi- sind, dasselbe zu leisten, kommen wir der Wahrheit naher ,, 



«Tnother series of experiments, that we also owe, in the first place, to Pfluger ( 84 

 Anouiei sci c i , . .. c i eava o-e The position of several 



consist in compressing the egg before and dunng its cleavage J _ 

 of the cleavage planes may be altered, yet a normal embryo J eT « lo ^ m 



STJS S^JS^-- valu of the ^--^ 

 in showing that the coincidence between the first cleavage planes and the orientmg pia 



