vi 
CONTENTS 
CHAPTER IV 
Tat Evipence or tue Respiratory APPARATUS 
Branchie considered as internal branchial appendages—Innervation of branchial 
The 
segments—Cranial region older than spinal—Three-root system of cranial 
nerves: dorsal, lateral, ventral—Explanation of van Wijhe’s segments— 
Lateral mixed root is appendage-nerve of invertebrate—The branchial 
chamber of Ammoccetes—The branchial unit, not a pouch but an appendage 
—The origin of the branchial musculature—The branchial circulation—The 
branchial heart of the vertebrate—Not homologous with the systemic heart 
of the arthropod—Its formation from two longitudinal venous sinuses— 
Summary 
CHAPTER V 
Tue EvipENCE oF THE THYROID GLAND 
value of the appendage-unit in non-branchial segments—The double nature 
of the hyoid segment—Its branchial part—Its thyroid part—The double 
nature of the opercular appendage—Its branchial part—Its genital part— 
Unique character of the thyroid gland of Ammocetes—Its structure— 
Its openings—The nature of the thyroid segment—The uterus of the 
scorpion—Its glands—Comparison with the thyroid gland of Ammoccetes— 
Cephalic generative glands of Limulus—Interpretation of glandular tissue 
filling up the brain-case of Ammoccetes—Function of thyroid gland— 
Relation of thyroid gland to sexual functions—Summary 
CHAPTER VI 
THE EvIpENCE oF THE OLFacToRY APPARATUS 
Fishes divided into Amphirhine and Monorhine—Nasal tube of the lamprey 
—Its termination at the infundibulum—tThe olfactory organs of the scorpion 
group—The camerostome—Its formation as a tube—Its derivation from, a 
pair of antenne—Its termination at the true mouth—Comparison with the 
olfactory tube of Ammoccetes—Origin of the nasal tube of Ammoccetes from 
the tube of the hypophysis—Direct comparison of the pie ceael tube with 
the olfactory tube of the scorpion group—Summary . . . 
CHAPTER VII 
Tue Prosomaric Secments or Limunus AND Its ALLIES 
Comparison of the trigeminal with the prosomatic region—The prosomatic 
appendages of the Gigantostraca—Their number and nature—Endognaths 
and ectognath—The metastoma—The coxal glands—Prosomatic region of 
Eurypterus compared with that of Ammoccetes—Prosomatic segmentation 
shown by marks on carapace—Evidence of ccelomic cavities in Limulus— 
Summary 
PAGE 
148 
185 
218 
233 
