XIV CONTENTS. 



PAGE 



mental results, the swallowing reflexes, 189; course of the nerve impulses in the 

 gustatory, chewing and swallowing reflexes, 189. II. The crossed thoracic 

 reflexes, 190. III. The crossed and uncrossed abdomino-thoracic reflexes, 190. 

 IV. Locomotion, 191. V. Equilibrium, 191. VI. Respiration, 191; respiratory 

 reflexes, 192; comparison with vertebrates, 193. VII. The cerebral hem- 

 spheres, 194. 



CHAPTER XII. 



THE HEART 195-209 



I. Location of the heart, 195. II. The development of the heart, 195; compari- 

 son of vertebrate and arachnid heart. III. The circulation, 198; arachnids, 198; 

 comparison with vertebrates, 198, direction of blood currents, aortic arches, carotids, 

 circle of Wellis, aortae, cardinals, curvature of heart, split posterior end, reduction 

 of cardiac area, and moulding effect of blood stream on structure of heart walls. 



IV. The cardiac nerves and ganglion, 200; the median cord or ganglion, 200; 

 the cardiac plexus, the lateral cardiacs, pericardials, segmental cardiacs. V. The 

 minute structure of the cardiac ganglion, 202; small multipolar or motor cells, 

 giant bipolar cells, small bipolar cells, motor terminals, 205; sensory terminals, 

 cardiac ganglia in vertebrates. VI. Experiments on the heart, 205. VII. Sum- 

 mary and conclusion, 208. 



THE NERVOUS SYSTEM AND SENSE ORGANS OF VERTEBRATES AND ARACHNIDS. GEN- 

 ERAL SUMMARY OF CHAPTERS I-XII 209-214 



CHAPTER XIII. 



THE EARLY STAGES OF ARTHROPOD AND VERTEBRATE EMBRYOS 215-248 



I. Primary causes of differential growth, 215. II. Morphological interpretation 

 of the early stages, 219. III. Embryology of limulus, 222; i. cleavage, 223; com- 

 parison with vertebrates, 223; 2. the germ disc or primitive cumulus, 224; 3. for- 

 mation of metameres, 225; 4. the gastrula, 227; 5. the germ wall, 228; 6. the meso- 

 derm, 230; the sources and kinds of mgsoderm: (a) procephalic, (b) postoral, (i) 

 axial cord, (2) mesoblastic somites, (3) lateral plates; the fibre cells, 232, give rise 

 to: (a) inter-tergal, branchial section of branchio-thoracic, and numerous scat- 

 tered, muscles; (b) to semi-amoeboid wandering cells which persist in adult stages; 

 Vascular area, 236; pellucid area. IV. The cephalic navel, dorsal organ, or neos- 

 toma, 238. V. Concrescence and the caudal navel or blastopore, 243. 



CHAPTER XIV. 



THE OLD MOUTH AND THE NEW; LOCOMOTOR AND RESPIRATORY APPENDAGES . . 249-273 

 The salient features of the mouth and appendages in arthropods and vertebrates, 

 249; the argument, 250. I. The closing of the old mouth, 251. II. The new 

 mouth, 253. III. The jaws or oral arches, 255; development of the oral arches 

 in the frog, 257; conclusion, 260. IV. The gill arches and the external gills, 261. 



V. The gill sacs, the thyroid and the thymus, 263. VI. The gut pouches, 266. 

 VII. The locomotor appendages, 263; conclusion, 271. 



CHAPTER XV. 



VARIATION AND MONSTROSITIES 274-288 



Problem stated. I. Invaginated appendages, 275. II. Asymmetry, 276. III. 

 Degeneration, 277; A. median fusion and antero-posterior degeneration, 277; 



