List of Lllustrations. 
Fig. 25. Perforation of the humerus (supra-condyloid foramen) in 
three species of Quadrumana where it normally occurs, 
and in Man, where it does not normally occur. . 
26. Antlers of stag, showing successive addition of branches 
in successive years 
27. Fission of a Protozodn . . : . . 
28. Hydra viridis, partly in section. . . . ms 
29. Successive stages in the division of the ovum, or egg-cell, 
ofa worm . ‘ . . . . . 
30. Ovarian ovum of a Moma r . . 
31. Amceboid movements of young egg-cells ° 
32. Human ovum, mature and greatly magnified 
33. Stages in the formation of the ai bodies in the ovum of 
a star-fish . : 
34. Fertilization of the ovum of an eauioteen a ‘ 
35. Fertilization of the ovum of a star-fish . . : . 
36. Karyokinesis of a typical tissue-cell (epithelium of Sala- 
mander) : 
37. Study of successive changes piaes pice} in the anelens 
of an epithelium-cell, preparatory to division of the cell 
38. Formation and conjugation of the pronuclei in Ascaris 
megalocephala . , 3 r : . 2 132; 
39. Segmentation of ovum . 
40. The contents of an ovum in an Advance stage of segmen- 
tation, drawn in perspective ‘ . 
41. Formation of the gastiula of Amphioxus . . : 
42. Gastrulation ‘ . ‘ 3 . é 
43- Gastrula of a Chalk one : F . . : 
44. Prophysema primordiale, an extant wecvenetoi . 
45. Ideal prim‘tive vertebrate, seen from the left side . 
. The same in transverse section through the ovaries . 
. Amphioxus lanccolatus 
. Balanoglossus 
. A large Sea-lamprey (Bapriowiioi MaArInNUs) « 
. Adult Shark (Carcharias melanopterius) 
. Diagram of heart and gill-arches of a fish 
. One gill-arch, with branchial fringe attached 
. Diagram of heart and gill-arches in a lizard 
. Ideal diagram of primitive gill- or aortic-arches 
. The same, modified for a bird 
. The same, modified for a mammal 
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