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.—Proso- 
matic sense organs.—F labellum.—Its structure and position.— Sense-organs 
of mandibles.—Auditory 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 Ammocetes.—Intrusion of glandular mass round brain into 
auditory capsule.—Intrusion of generative and hepatic mass round brain 
into base of fiabellum.—Summary. 
WHEN speaking of the tripartite arrangement of the cranial nerves, 
an arrangement which gave the clue to the meaning of the cranial 
segments, I spoke of the trigeminal as supplying the sensory nerves 
to the skin in the head-region, and I compared this dorsal system 
of afferent nerves to the system of epimeral nerves in Limulus which 
supply the prosomatic and mesosomatic carapaces of Limulus with 
sensory fibres. I compared the ventral system of eye-muscle nerves 
with the system of nerves supplying the segmental dorso-ventral 
somatic muscles of the prosomatic region, and I compared the lateral 
system of mixed nerves with the nerves supplying the prosomatic 
and mesosomatic appendages of Limulus. I compared, also, the 
optic nerves and the olfactory nerves with the corresponding nerves 
in the same invertebrate group. My readers will see at once that one 
well-marked group of nerves—the auditory and lateral line system— 
has been entirely omitted up to the present, it has not even been 
mentioned in the scheme of the cranial segments; I have purposely 
reserved its consideration until now, because the organs these nerves 
supply, though situated in the skin, are of such a special character 
