TABLE OF CONTENTS. 5 



Page 

 Organs of circulation . . . . . , '' .69 



Heart 61 



Arteries and veins 62 



Heart and vessels of vertebrates 64 



Organs of respiration, . , . 67 



Branchiae 69 



Lungs, trachere. ..... .... 69 



Tracheal gills . . . t - , .- . . .71 



Renewal of external medium ... r ... 72 

 Venous and arterial blood . .. . , . . . .73 



Animal heat. , . . . . . . c . .73 



Organs of secretion - ... 74 



Kidneys 75 



Water- vascular vessels and segmental organs . : . . .75 

 Vertebrate kidneys . . . . . . . : . .76 



Cutaneous glands : . . 77 



ORGANS OF ANIMAL LIFE . ... . .=.'-. .78 



Skeletal structures - - - ....... 79 



Nervous system . . : . . 79 



Sense organs. . 83 



Tactile organs . . : . . ..... 84 



Auditory organs : : . 85 



Visual organs . . t . . . . . . . .85 



Facetted eye . . . . . . . . . . . 88 



Simple eye ... 89 



Olfactory organs . . . . . . . . . . 91 



INTELLIGENCE AND INSTINCT 93 



REPRODUCTIVE ORGANS . . . . . . . . .95 



Biogenesis . . . . . . .,.;.,.-. . .96 



Asexual reproduction. . .... 96 



Sexual reproduction . . . . ; . . ..' '. .97 



Hermaphroditism . . ..-. 99 



Separation of the sexes 100 



Sexual differences . . . . , 101 



Sexual dimorphism . . . , 104 



Parthenogenesis . . . . . ' 105 



DEVELOPMENT .... . . . . . .107 



Fertilisation of the ovum . 108 



Segmentation of the ovum .110 



Food-yolk Ill 



Blastosphere . . . . 113 



Formation of gastrula . . .114 



Primitive streak . . . . . . ... . .115 



Germinal layers . . . . . . . . . . 116 



Theory of Gastraea ... . 117 



DIRECT DEVELOPMENT AND METAMORPHOSIS 119 



Effect of food-yolk on development 120 



Explanation of Metamorphosis . . . . . . .121 



ALTERNATION OF GENERATIONS, POLYMORPHISM AND HETEROGAMY 123 



Metagenesis . . 123 



Explanation of Metagenesis . . . . . . .124 



Polymorphism . . . .126 



Heterogamy . . . . , . . ... . .127 



Pasdogenesis . . . . . . . . . .128 



Heterogamy of Trematoda 120 



