Xo. 5S4] 



B1LA TERA LITY IX V EltTEHl: . 1 TES 



507 



plane of the embryo often deviated widely from the first 

 or second cleavage planes. We accordingly undertook 

 amextended series of observations on the living segment- 

 ing eggs of Amblystoma, Diemyctylus, Rana and Bufo. 

 Our conclusions were as follows : 



The later observations by Gronroos, v. Ebner, Morgan 

 and Tsuda, Kopsch and others have likewise emphasized 

 the significance of these variations. 



It is scarcely necessary to state that if these cleavage 

 planes mark embryonic areas, the amount of material 

 set apart in different eggs for similar parts of their re- 

 spective embryos, must be exceedingly variable, and these 

 excesses and deficiencies must be corrected by a corre- 

 sponding re tarded or accelerated growth until the norm 

 is reached, but there is not the slightest evidence that 

 Mid, corrections occur. 



not onlv in various amphibia but also' in practicallv all 

 classes of vertebrates: in Amphioxus by Wilson; in 

 Petromyson by McClure, Kupffer, Eycleshymer ; in Dip- 

 noans by Semon; in Ganoids by Salensky, Dean, Whit- 

 man and Eycleshymer; in Teleosts by Coste, Hoffmann, 

 His, Agassiz and Whitman, King-ley and Conn. Clapp, 

 Sobotta and others; in Eeptiles by Agassiz and Clark, 

 Oppel, Sarasin; in Aves by Coste, Koelliker, Kionka ; 

 in Mammals by Duval, v. Beneden, Assheton, Sobotta 



The inevitable conclusion from such a mass of evi- 

 dence can not be other than that neither the position or 

 direction of cleavage grooves has the slightest signifi- 

 cance as far as the setting apart of definite embryonic 

 areas is concerned. 



If then it may be considered an established fact that 



