70 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



only for the general symmetry of themselves and of their 

 isolated parts, and another sort of possible structure of 

 the egg-protoplasm which we now shall have to consider, 

 and which, at the first glance, seems to form a serious 

 difficulty to our statements, as far at least as they claim 

 to be of general importance. The study of this other sort 

 of germinal structure at the same time will lead us a 

 step farther in our historical sketch of the first years of 

 " Entwickelungsmechanik ' and will bring this sketch to 

 its end. 



ON SOME SPECIFICITIES OF ORGANISATION IN CERTAIN GERMS 



It was known already about 1890, from the careful 

 study of what has been called " cell-lineage," that in the 

 eggs of several families of the animal kingdom the origin 

 of certain organs may be traced back to individual cells of 

 cleavage, having a typical histological character of their own. 

 In America especially such researches have been carried 

 out with the utmost minuteness, E. B. Wilson's study of 

 the cell-lineage of the Annelid Nereis being the first of 

 them. If it were true that nuclear division is of no 

 determining influence upon the ontogenetic fate of the 

 blastomeres, only peculiarities of the different parts of 

 the protoplasm could account for such relations of special 

 cleavage cells to special organs. I advocated this view 

 as early as in 1894, and it was proved two years later by 

 Crampton, a pupil of Wilson's, in some very fine experi- 

 ments performed on the germ of a certain mollusc. 1 The 

 egg of this form contains a special sort of protoplasm near 



1 Arch. Enttv. Mech. 3, 1896. 



