TABLE OF CONTENTS. 5 



Page 

 Organs of circulation . .... ^ ... 59 



Heart 61 



Arteries and veins 62 



Heart and vessels of vertebrates 64 



Organs of respiration ... ...... 67 



Branchiae 69 



Lungs, tracheae .... 69 



Tracheal gills .... . 71 



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



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



Animal heat. . . 73 



Orrja >is of secretion , ... 71 



Kidneys 75 



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



Vertebrate kidneys . . 76 



Cutaneous glands ' . . 77 



ORGANS OP ANIMAL LIFE ... 78 



Skeletal structures - , .... . . 79 



Nen-ous system . . 79 



Sense organs. . . 83 



Tactile organs . . 84 



Auditory organs 85 



Visual organs . . c 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 Gastrrca 117 



DIRECT DEVELOPMENT AND METAMORPHOSIS 119 



Effect of food -yolk on development 120 



Explanation of Metamorphosis 121 



ALTERNATION OP GENERATIONS, POLYMORPHISM AND HETEROGAMY 123 



Metagenesis 123 



Explanation of Metagenesis 124 



Polymorphism 126 



Heterogamy 127 



Predogenesis 128 



Heterogamy of Trcmatocla 12'J 



