CONTENTS vii 
CHAPTER VIII 
THE SEGMENTS BELONGING TO THE TRIGEMINAL NeRvE-GRouP 
PAGE 
The prosomatic segments of the vertebrate—Number of segments belonging to 
the trigeminal nerve-group—History of cranial segments—Eye-muscles and 
their nerves—Comparison with the dorso-ventral somatic muscles of the 
scorpion—Explanation gf the oculomotor nerve and its group of muscles— 
Explanation of the trochlear nerve and its dorsal crossing—Explanation 
of the abducens nerve—Number of segments supplied by the trigeminal 
nerves—Hvidence of their motor nuclei—Evidence of their sensory ganglia 
—Summary . ‘ a ‘ ‘ : ‘: ‘ é 3 ‘ % . 257 
CHAPTER IX 
THe Prosomatic SEGMENTS oF AMMOC@TES 
The prosomatic region in Ammoccetes—The suctorial apparatus of the adult 
Petromyzon—Its origin in Ammoccetes—Its derivation from appendages— 
The segment of the lower lip or the metastomal segment—The tentacular 
segments—The tubular muscles—Theit segmental arrangement—Their 
peculiar innervation—Their correspondence with the system of’ veno-peri- 
cardial muscles in Limulus—The old mouth or paleostoma—The pituitary 
gland—Its comparison with the coxal gland of Limulus—Summary . . 286 
CHAPTER X 
Tue RELATIONSHIP OF AMMOCHTES TO THE MOST ANCIENT FISHES 
—THE OSTRACODERMATA 
The nose of the Osteostraci—Comparison of head-shield of Ammoccetes and of 
Cephalaspis—Ammoceetes only living representative of these ancient fishes 
—Formation of cranium—Closure of old mouth—Rohon’s primordial 
cranium—Primordial cranium of Phrynus and Galeodes—Summary . . 3826 
CHAPTER XI 
THE EVIDENCE OF THE AUDITORY APPARATUS AND THE ORGANS OF 
THE LATERAL LINE 
Lateral line organs—Function of this group of organs—Poriferous sense-organs 
on the appendages in Limulus—Branchial sense-organs—Prosomatic sense- 
organs—F labellum—Its structure and position—Sense-organs of mandibles 
—aAuditory organs of insects and arachnids—Poriferous chordotonal organs— 
Balancers of Diptera—Resemblance to organs of flabellum —Racquet-organs 
of Galeodes—Pectens of scorpions—Large size- of nerve to all these special 
sense-organs—Origin of parachordals and auditory capsule—Reason why 
VIIth nerve passes in and out of capsule—Evidence of Ammoccetes— 
Intrusion of glandular mass round brain into auditory capsule—Intrusion 
of generative and hepatic mass round brain into base of flabellum— 
Summary) 2... ee BBE 
