188 A. A. W. TTUr.K'KCIIT. 



been hitherto adhered to, but by whicli latter nobody has as 

 yet succeeded in clearing up the actual phylof^enesis of these 

 foetal membranes. 



Full and extensive investigations of all those numerous 

 genera of mamuials that have not yet been examined will, I 

 hope, in due time give us occasion to complete or to modify the 

 views here advocated. 



It was a great pleasure to me to offer them, tentatively, in 

 an address which I was invited to give in the section of 

 embryology of this Seventh International Congress — a section 

 which, with good right, has been called into life for the first 

 time at this meeting in Boston. Embryological problems 

 have been attacked by American investigators with wonder- 

 ful results, and the lucidity of exposition that is characteristic 

 of so many of your embryological workers is only equalled 

 by the beautiful transparency of the eggs of those marine 

 animals on which so many important researches on cell-lineage 

 have been conducted. 



That I have been less clear is not only a congenital defect, 

 but is parallel with the utter hopelessness of our expecting 

 that we shall ever be able to follow the cell-lineage in the 

 deeply hidden and exceedingly small mammalian eggs. Still, 

 a full knowledge of that very cell-lineage would be eminently 

 decisive for many of the questions that have occupied us in 

 the course of this address, to which you have listened with so 

 much patience. 



