283 



14) Derselbe, Beitr. 1 z. Entw.-Mech.: Einleitung und : Zur Orientirung 

 über einige Probleme der embryonalen Entwickelung. Zeitschr. f. 

 Biologie, Bd. XXL München 1885. 



15) Böen, Gust., Ueber Druckversuche an Froscheiern. Anat. Anz., 1893, 

 Bd. VIII, S. 609—627. 



Nachdruck verboten. 



Studies in Morphogenesis. II. 



Regeneration in Obelia and its Bearing on Differentiation in 



the Germ-Plasma 1 ). 



By C. B. Davenport, Instructor in Zoology at Harvard College. 

 With 6 figures. 



I. Statement of Problem. 



That development in budding and in regeneration, like develop- 

 ment from the egg, depends upon the pre-existence of embryonic 

 tissue — i. e. tissue which has never been differentiated — is one 

 of the oldest and most fundamental assumptions of theories of here- 

 diti. The conception that development in these cases takes place 

 from a split-off piece of the fertilized ovum seems to simplify the 

 problem why the thing produced resembles some part, at least, of 

 that developed from the fertilized ovum. 



The point of most considerable disagreement among modern 

 theorists involves quite a different question ; namely, whether embryonic 

 tissue is qualitatively different in different parts of the body, — has 

 the potentiality of producing only very definite and distinct things 

 independent of environment, or whether it is potentially the same in 

 all parts of the body, the difference in the result of development 

 depending upon agencies outside the developing cell 2 ). 



This difference of opinion may be applied to a specific case. It 

 is well known that hydroids possess to a great degree the capacity 



1) Contributions from the Zoological Laboratory of the Museum of 

 Comparative Zoology, E. L. Mabk Director, No. XL. 



2) Thus Weismann [„Das Keimplasma", p. 141] says concerning the 

 embryonic tissue from which the regenerating arm of the Salamander is 

 about to arise, that what shall be produced „hängt nicht von ihrer zu- 

 fälligen Lagerung oder von sonstigen äußeren Einwirkungen ab, sondern 



20* 



