LIST OF ILLUSTRATIONS. 



INTRODUCTORY CHAPTER 



rid. PAGE 



1. Stages in the maturation of the egg of the frog. (After O. Schultze) 9 



2. Segmentation of the egg of Amphioxus. (After Hatschek) . . 18 



3. Segmentation of the frog's egg 20 



4. The hen's egg, freshly laid 21 



5. Segmentation of the germinal disc of the hen's egg. (After Coste 



and Duval) 21 



6. Later stage in the segmentation of the germinal disc of the hen's 



egg. (After Coste and Duval) . , 21 



7. Vertical section of the germinal disc of the hen's egg at the close of 



segmentation. (After Duval) . . . " . . . .21 



8. Vertical section of early larval stage of Amphioxus. (After Hats- 



chek) 23 



9. Horizontal section of early larval stage of Amphioxus. (After Hats- 



chek) 23 



10. Transverse section through the head of a chick embryo at the end of 



the first day of incubation .24 



AMPHIOXUS 



11. Young specimen of Amphioxus, viewed as a transparent object. 



(From Marshall and Hurst) 38 



12. Transverse section through the anterior part of the pharynx of an 



adult Amphioxus. (From Marshall and Hurst) .... 39 



13. Transverse section through the posterior part of the pharynx of an 



adult female Amphioxus. (From Marshall and Hurst) . . 42 



14. Segmentation of the egg of Amphioxus. (After Hatschek) . . 50 



15. Formation of the gastrula of Amphioxus. (After Hatschek) . . 53 

 1 (). Later stage in the formation of the gastrula of Amphioxus. (After 



Hatschek) 53 



17. Further stage in the formation of the gastrula of Amphioxus. (After 



Hatschek) ... . . 64 



18. Completion of the gastrula of Amphioxus. (After Hatschek) . . 54 

 ID. The gastrula of Amphioxus, bisected vertically. (After Hatschek) . 65 

 20. The gastrula of Amphioxus, bisected horizontally. (After Hatschek) 5> 

 21-24. Transverse sections across the bodies of Amphioxus embryos, 



showing the mode of formation of the nervous sj'stem and of 



the mesoblastic somites. (After Hatschek) .... 68 



