FIG. 61. NUCLEI FROM RABBIT EMBRYOS. 1-4, age, seven and one half days; 



5-8, age, ten days. 9-20, age, twelve and one half days. 21-33, age, sixteen 



and one half days. 



I, ectoderm ; 2, mesoderm ; 3, entoderm ; 4, Hensen's knot; 5, ento- 

 derm; 6, mesenchyma; 7, entoderm; 8, medullary groove; 9, ectoderm; 

 10, large motor neurone; n, spinal ganglion; 12, mesenchyma; 13, 

 cartilage; 14, Wolffian body; 15, kidney; 16, striated muscle; 17, heart 

 muscle; 18, esophageal entoderm; 19, tracheal entoderm; 20, liver; 21, 

 ectoderm; 22, motor neurone; 23, spinal ganglion; 24, dermis; 25, 

 hypodermis; 26, cartilage; 27, 28, Wolffian tubules; 29, pelvis of kid- 

 ney; 30, heart muscle; 31, esophageal entoderm; 32, tracheal entoderm; 

 33, liver. 



176 



