viii ILLUSTRATIONS 



FIGURE PAGE 



18. Cross-Section of the Root of a Hair . . . .61 



19. Cross-Section of a Lingual Muscle Fibre of the 



Moccasin Snake ....... 62 



20. Part of a Muscle Fibre of the Human Tongue . . 62 



21. Section of a Human Retina ..... 63 



22. Motor Nerve Cells of Various Mammals ... 66 



23. Group of Five Nerve Cells from the First Cervical 



Ganglion of a Child at Birth .... 68 



24. Group of Four Nerve Cells from the First Cervical 



Ganglion of a Man Dying of Old Age, at 92 Years 69 



25. Life History of Blood Corpuscles, Rabbit Embryos . 78 



26. Four Tadpoles of the European Frog ... 88 



27. Curves Showing the Growth of Boston School Children 



in Height and Weight . . . . .91 



28. Curves Showing the Daily Percentage Increments in 



Weight of Male Guinea-Pigs . . 94 



29. Curves Showing the Daily Percentage Increments in 



Weight of Female Guinea-Pigs . . 96 



30. Curves Showing the Length of Time Required to Make 



Each Successive Increase of Ten per Cent, in 

 Weight by Male Guinea-Pigs v . ' . . .97 



37. Curves Showing the Length of Time Required to Make 

 Each Successive Increase of Ten per Cent, in 

 Weight by Female Guinea-Pigs . . . 98 



32. Curves Showing the Growth of Man from Birth to 



Maturity ........ 99 



33. Curves Showing the Daily Percentage Increments in 



Weight by Male Chickens 101 



34. Curves Showing the Daily Percentage Increments in 



Weight by Female Chickens .... 102 



