Anachronisms Show Local Relations Inessential 67 
of the medullary tube. These modes of behavior and 
others like them indicate that the parts which continue to 
develop normally require for their development neither 
the absent parts, nor that the remaining parts should be 
at the stage of development normally corresponding, and 
thus that they can develop alone, independent to a cor- 
responding extent of those absent or backward.” 4! 
“Anachronisms of development,” continues Roux in 
a later research, “appear also in the relative retardation 
or acceleration of development of one of the germ layers 
in relation to the others. For example several embryos 
otherwise normal, in which the medullary fold is still 
quite undifferentiated, show already in the mesoderm, in 
the entoderm, and in the chorda dorsalis, formations 
which appear normally only about the time of closure of 
the medullary tube. In this case there is an evident re- 
tardation of development of the ectoderm in relation to 
the development of the other two layers. There occur 
also inequalities of lesser degree in the rapidity of 
development of the two lateral halves of the body, and 
thus it is possible to observe two different stages of 
development in the same object.” * 
“Tf such large parts of the organism,” concludes our 
author in a still later study, “can remain behind in their 
development or indeed remain absent, without thereby 
producing any disturbance in the development of the 
others, it follows surely that the development of these 
414Wilhelm Roux: Zur Orientierung iiber einige Probleme der 
embryonalen Entwicklung. Zeitschrift fiir Biologie. Bd. XXI. 
Miinchen, Jul 1885. P. 478—479. Gesamm. Abhandl. Zw. Bd. P. 
203—204. 
42Wilhelm Roux: Uber die ktinstliche Hervorbringung halber 
Embryonen, usw. Virchows Archiv, P. 128—129. Gesamm, Abhandl. 
Zw. Bd. P. 438. 
