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.*° 
“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 
“Wilhelm Roux: Uber die ersten Teilungen des Froscheies und 
ihre Beziehungen zu der Organbildung des Embryo. Anatomischer 
Anzeiger, Band VIII. 1893. N. 18. P. 608—609. Gesamm. Abhandl. 
Zw. Bd. P. 926. 
