CONTENTS. IX 



CHAPTER IX. 



PAGE 



Organs of Respiration 135 



Respiration, 135 — Structure and arrangement of the gills, 136 — 

 Pseudobranchise, 140 — Accessory respiratory organs, 142 — 

 Air-bladder ; its varieties, structure, and functions, 142. 



CHAPTER X. 



Organs of Circulation 150 



CHAPTER XL 

 Urinary Organs 155 



CHAPTER XII. 

 Organs of Reproduction 157 



Fishes are dioecious, 157 — Hermaphroditism, 157 — Oviparous and 

 viviparous fishes, 157 — Generative organs of Branchiostoma, 

 157 — of Cyclostomes ; their ova, 158 — Female organs of 

 Teleosteans and their ova, 158 — Instances of females taking 

 care of their progeny, 160 — Male organs of Teleosteans, 162 — 

 Instances of males taking care of their progeny, 163 — Genera- 

 tive organs of Ganoids, 163 — of Choudropterygians and their 

 ova, 166. 



CHAPTER XIII. 

 Growth and Variation of Fishes . . , .170 



Changes of form of the body or certain parts, normally accompany- 

 ing gi'owth, 170 — Changes dependent on sexual development, 

 176 — Secondary sexual differences, 176 — Mixogamous, poly- 

 gamous, and monogamous fishes, 177 — Hybridism as a cause 

 of variation, 178 — Regular and irregular growth of fishes, 178 

 — Leptocephali not a normal state of development, 179 — 

 Changes of colour of the muscles and external parts ; chroma- 

 tophors, 182 — Albinism, 183. 



