CHAPTEB 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. — Flabellum. — Its structure and position. — Sense-org*ans 

 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-org-ans. — Origin of parachordals and 

 auditory capsule. — Reason why Tilth nerve passes in and out of capsule. — 

 Evidence of Ammocoetes. — Intrusion of glandular mass round brain into 

 auditory capsule. — Intrusion of generative and hepatic mass round brain 

 into base of flabellum. — 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 



