404 T. H. MORGAN AND UME TSTJDA. 



termiue experimentally exactly the process that takes place in 

 the dorsal lip of the blastopore, and then we shall be prepared 

 to formulate more definitely a theory of overgrowth. 



Bkyn Mawk, Pa., U.S.A., 

 May 22nd, 1893. 



DESCRIPTION OF PLATES 24 & 25, 



Illustrating Messrs. T. H. Morgan and Ume Tsuda's paper 

 on " The Orientation of the Frog's Egg." 



Figs, iv, v, vi, vii, viii, ix, x, xi, xii, xni, Uana temporaria. 

 Figs, i, ii, hi, xiv, xv, xvi, xvii, xvhi, xix, xx, Rana, sp. ? 



PLATE U. 



Fig. 1. — View of 32-celled stage from above. 

 Fig. II. — View of same stage from dark side. 

 Fig. Ill, — View of same stage from light side. 

 Fig. IV. — View of blastula (about 150 cells), dark side. 

 Fig. v. — View of same, light side. 



Fig. VI. — Four-celled stage, lower pole; M — iV, first furrow. 

 Fig. VII. — About 100-celled stage, lower pole. 

 Fig. VIII. — About 100-celled stage, lower pole. 

 Fig. IX. — Earlier stage than last. 



Fig. X. — View of lower pole of egg at end of segmentation. 

 Fig. XI. — Early blastopore stage. Pigment has somewhat shifted its 

 earlier distribution, lower pole. 

 Fig. XII. — Early blastopore stage, lower pole. 

 Fig. XIII. — Early blastopore stage, side view. 

 Fig. XIV.— Embryo with unclosed blastopore, seen from in front. 

 Fig. XV. — Same from below. 



Fig. XVI. — Embryo with unclosed blastopore, seen from in front. 

 Fig. xvii. — Embryo with unclosed blastopore, seen from in front. 



