CONTENTS. IX 



TAGB 



Touch). Outer Skin (Epidermis) and Leather-skin (Cortttm). 

 Appendages of the Epidermis : Skin-glands (Sweat-glands, Tear- 

 glands, Sebaceous Glands, Milk-glands); Nails and Hair. The 

 Embryonic Wool-covering. Hair of the Head and of the Beard. 

 Influence of Sexual Selection. Arrangement of the Nerve-system. 

 Motor and Sensory Nerves. Central Marrow : Brain and Dorsal 

 Marrow. Constitution of the Human Brain : Large Brain (Cerw- 

 brum) and Small Brain (Cerebellum). Comparative Anatomy of 

 the Central Marrow. Germ-history of the Medullary-tube. Sepa- 

 ration of the Medullary-tube into Brain and Dorsal Marrow. 

 Modification of the Simple Brain-bladder into Five Consecutive 

 Brain-bladders: Fore-brain (Large Brain, or Cerebrum), Twixt- 

 brain ("Centre of Sight"), Mid-brain (" Four Bulbs "), Hind-brain 

 (Small Brain, or Cerebellum), After-brain (Neck Medulla). Various 

 Formation of the Five Brain-bladders in the various Vertebrate 

 Classes. Development of the Conductive Marrow, or " Peripherie 

 Nervous System" ... ... ... ... ... ... 190 



CHAPTER XXL 



DEVELOPMENT OF THE SENSE-ORGANS. 



Origin of the moat highly Purposive Sense-organs by no Preconceived 

 Purpose, but simply by Natural Selection. The Six Sense-organs 

 and the Seven Sense-functions. All the Sense-organs originally 

 Developed from the Outer Skin-covering (from the Skin-sensory 

 Layer). Organs of the Pressure Sense, the Heat Sense, the 

 Sexual Sense, and the Taste Sense. Structure of the Organ of 

 Scent. The Blind Nose-pits of Fishes. The Nasal Furrows change 

 into Nasal Canals. Separation of the Cavities of the Nose and 

 Mouth by the Palate Roof. Structure of the Eye. The Primary 

 Eye Vesicles (Stalked Protuberances from the Twixt-brain). 

 Inversion of this Eye Vesicle by the Crystalline Lens, separated 

 from the Horn-plate. Inversion of the Vitreous Body. The Vas. 

 cular Capsule and the Fibrous Capsule of the Eyeball. Eyelidt. 

 Structure of the Ear. The Apparatus for Perception of Sound : 

 Labyrinth and Auditory Nerve. Origin of the Labyrinth from 

 the Primitive Ear Vesicles (by Separation from the Horn-plate). 

 Conducting Apparatus of Sound : Drum Cavity, Ear Bonelets, and 

 Drum Membrane. Origin of these from the First Gill-opening 

 and the Parts immediately round it (the First and Second Gill- 

 arch). Rudimentary Outer Ear. Rudimentary Muscles of the 

 Ear-shell ... 233 



