vi CONTENTS 



CHAPTER IV 

 The Evidence of the Respiratory Apparatus 



r.\r, i. 



Branchiae considered as internal branchial appendages — Innervation of branchial 

 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 Amniocoetes — 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 148 



CHAPTER V 

 The Evidence of the Thyroid Gland 



The 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 Ammoccetes — 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 .... 185 



CHAPTER VI 



The Evidence of the Olfactory Apparatus 



Fishes divided into Amphirhime and Monorhins — Nasal tube of the lamprey 

 —Its termination at the infundibulum — The olfactory organs of the scorpion 

 group — The camerostome — Its formation as a tube — Its derivation from a 

 pair of antennae — 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 hypophysial tube with 

 the olfactory tube of the scorpion group — Summary 218 



CHAPTER VII 



The Prosomatic Segments of Limulus 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 233 



