66 Indications of a Central Zone of Development 



respective formative capacity, because it would leave un- 

 altered the reciprocal relations of the different parts in 

 each network. 



Further, the deformations which the entire organism, 

 and consequently also each of its different networks, 

 undergo, would not seem to alter markedly the internal, 

 reciprocal relations of the different parts of each net- 

 work; thus from frog's eggs which had been compressed 

 continuously during their development, the blastula and 

 gastrula having been forcibly flattened, folded, and bent, 

 there developed embryos whose internal and external 

 aspect was just the same as though they had been allowed 

 from the first to develop in a normal fashion and had 

 undergone the deformation only later. 40 



"In the development of frog's eggs it happens very 

 often," Roux writes further, "that the primitive mouth 

 of the gastrula is not yet closed when the medullary folds 

 appear, and this condition can persist in part up till the 

 time of the closure of the medullary tube and the forma- 

 tion of the branchial elevations and adhesion cups. The 

 formation of these latter can proceed in a manner which 

 appears quite normal in the anterior half of the body even 

 though the posterior half of the body may have quite an 

 abnormal form, the primitive mouth remaining persist- 

 ently wide open. Another instance, yet more surprising, 

 is that in which notwithstanding the entire absence of the 

 medullary ridges, the gastrula gradually exchanges its 

 round form for a pear shaped one, a thing which or- 

 dinarily occurs only after the formation and development 



40 Wilhelm Roux : Uber die ersten Teilungen des Froscheies und 

 ihre Beziehungen zu der Organbildung des Embryo. Anatomischer 

 Anzeiger, Band VIII. 1893. N. 18. P. 608609. Gesamm. Abhandl. 

 Zw. Bd. P. 926. 



