302 Charles Zeleny. 



The localization of morphogenic factors. Only two fragments 

 were allowed to develop Into larvae, and neither of these showed a 

 sufficient differentiation for our purpose. One larva Is a solid 



Fjg. 5 (x 216). 



A, larva developed from a one-half vertical fragment of an unfertilized 

 egg; age 49 hours. B, eight-cell stage of a fragment of a fertilized egg ( — 2/3 

 of an egg), obtained by a vertical cut before the formation of the first polar 

 body; except for the unusual cross furrows the cleavage resembles a normal 

 whole one. 



ciliated mass of cells and the other, shown In Figure 5A, has an 

 Internal cavity with a few free mesenchyme cells. 



II. Fertilization to complete separation of the first polar body. 

 The limits include the period between the entrance of the sperma- 

 tozoon and the complete separation of the first polar body (Fig. 

 6). Seven eggs were operated on, but only two of these devel- 

 oped beyond the two-cell stage. The one clear case bearing on 

 the localization of cleavage factors (Fig. 5B) shows a typical 

 whole cleavage at the eight-cell stage. The morphogenic factors 

 receive no light from the one early blastula obtained. 



III. First polar body to complete separation of second polar 

 body. The limits of this period are represented by the separa- 

 tion of the first polar body on the one hand and of the second 

 polar body on the other (Fig. 7), Nineteen eggs were operated 

 on, seven by horizontal, ten by vertical and two by oblique cuts. 

 The cases that bear on cleavage factors show In nearly every In- 

 stance some departure from the normal whole cleavage as regards 

 size, position or division rhythm of cells. The direction of the 

 cut seems, however, not to influence the character of the defect, 



