58 



The Chromatin in the Development of Hybrids 



EXPLANATION OF PLATES. 

 PLATES I TO IV. 



ABBREVIATIONS. 



bVpo., Blastopore. 

 cd., Chorda. 

 ec'drm., Ectoderm. 

 emb., Embryo. 

 en'drm., Endoderm. 

 In^., Lens. 

 nis^drm., Mesoderm. 

 pi'bl.. Periblast. 

 ylTc., Yolk. 



PLATE I. 



Fig. 1. Conjugation of pronuclei in a dispermic Fundulus hybrid egg. 



Fig. 2. Cross section of a Fnndulus hybrid embryo that was nearing' the 

 closure of the " blastopore." It shows the ectodemi, endoderm, meso- 

 derm, neural cord, chorda and periblast. 



Fig. 3. Horizontal section through the eye of a Fundulus hybrid embryo 

 that had come to the close of its development. Very few of the cell 

 boundries can be made out. Cells of the cup are arranged in more or less 

 distinct rows. Nucleoli numerous and large. One cell in the lens in the 

 process of division. 



Figs. 4, 5, 6 and 7. Caudal end of four Fundulus hybrid embryos which 

 had come to the close of their development. Shows four types of 

 abnormal " blastopore " closure. 



