6 CONTENTS 



Page 



XXI. Respiration 312 



XXII. Respiration in Lowek Animals 340 



XXIII. Excretion . 352 



XXIV. Skin Structure AND Excretion IN THE Lower Animals 374 

 XXV. The Nervous System . . .... . 383 



XXVI. The Nervous System (continued) 411 



XXVII. The Nervous System in the Lower Anijuls . 429 



XXVIII. The Special Senses 436 



XXIX. The Special Senses (continued) 452 



XXX. The Special Senses (concluded) 470 



XXXI. Sensation in the Lower Animals 480 



XXXII. The Voice 486 



XXXIII. Bacteria and Sanitation 493 



Index 505 



