CONTENTS. IX 



>AGH 



Touch). — Outer Skin (Epidermis) and Leather-skin (Corium). — 

 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 (Cere- 

 brum) t,n& 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 Yertebrate 

 Classes. — Development of the Conductive Marrow, or "Peripheric 

 Nervous System" ... ... ... ... ... ... 19C 



CHAPTER XXI. 



DEVELOPMENT OF THE SENSE-ORGANS. 



Origin of the most 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. — Eyelid*. 

 — 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 



