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." 41 



"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." 42 



"If 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 



"Wilhelm Roux: Zur Orientierung iiber einige Probleme der 

 embryonalen Entwicklung. Zeitschrift fur Biologic. Bd. XXI. 

 Miinchen, Jul 1885. P. 478479. Ges-amm. Abhandl. Zw. Bd. P. 

 203204. 



* 2 Wilhelm Roux: Uber die kiinstliche Hervorbringung halber 

 Embryonen, usw. Virchows Archiv, P. 128 129. Gesamm. Abhandl. 

 Zw. Bd. P. 438. 



