Localization of the N emertine Egg. 



307 



cells or rhythm of division (Figs. loA, B, C) up to a case with 

 an open cup-shaped blastula of a purely partial type (Fig. loE). 

 The results give no definite relation between the position of the 

 removed portion of the egg and the character of the resulting 

 defect in cleavage. A possible instance of such a relation is shown 

 in a sixteen-cell stage developed from a vertical-oblique fragment, 

 which show^s a corresponding flattening of one side of the embryo 

 (Fig. loC). ■ 



Fig. 10 (x 216). 



Fragments Obtained from Eggs 7vifli Two Polar Bodies Before the Lateral Elonga- 

 tion of the Cell. 



A, eight-cell ( — ) stage of fragment (3=2/3 of egg), obtained by a vertical 

 (slightly oblique) cut; oblique view. Note that the cells of the upper quartet 

 are smaller than those of the lower (the reverse of the normal condition) and 

 that one of the quadrants is behind the others in its division. B, 15-16-ceIl stage 

 of fragment (=1/2 of egg), obtained by an oblique cut; side view. Note that 

 the cells differ from normal whole ones in rhythm of division and size rela- 

 tions. C, i6-cell stage of a fragment (=22/;^ of egg), obtained by vertical- 

 oblique cut; side view. Note oblique flattening of egg. D, larva (50 hours 

 old) from fragment (:r=2/3 of egg), obtained by a vertical cut; side view. 

 Note solid enteron and absence of apical plate. E, open, partial blastula from 

 a fragment (3=2/3 of egg), obtained by a vertical cut; oblique view from 

 open side. 



