EXPERIMENTAL STUDIES ON GERMINAL 

 LOCALIZATION. 



BY 



EDMUND B. WILSON.. 



I. THE GERM-REGIONS IN THE EGG OF DENTALIUMi. 



With ioo Figxjres. 

 CONTENTS. 



I. Introduction. 



II. Preliminary Observations on the un segmented Egg and the normal 



Development. 



III. Effect of removing the Polar Lobe. 



(a) General history of the lobeless Embryo, with a Comparison of 



isolated Blastomeres. 



(b) The Mesoblast Question. 



IV. Localization of the apical Organ, and its Correlation with the post-trochal 



Region. 



V. Localization in the unsegmented Egg. 



(a) Development of Fragments obtained by horizontal or oblique Sec- 



tion. 



(b) Development of Fragments after vertical Section. 



VI. Observations on enucleated Fragments of fertilized Eggs and on the 



isolated Polar Lobe. 



VII. Comment. 



VIII. Summary. 



INTRODUCTION. 



The following experimental studies are offered as a contribu- 

 tion to the theory of "Organbildende Keimbezirke" or germinal 

 prelocalization, especially as applied to the cytoplasmic regions of 

 the unsegmented egg. Following the enunciation of the principle 

 of "precocious segregation" by Ray Lankester, in 1877, the im- 



iThis work was carried out at the Naples Zoological Station between February 

 and August, 1903, on a grant from the Carnegie Institution of Washington, in 

 which was included the use of one of the tables subscribed for by the Institution. 

 My best thanks are due to the administration of the station for the unfailing 

 efficiency and courtesy with which my work was aided in every possible way. 



