ILLUSTRATIONS 



FIO. PAGE 



1. HYOID ARCH OF THE CONGER. (ORIGINAL.) . . 58 



2. "VERTEBRA" OF A PLEURONECTID. (GEOFFROY.) . . 61 



3. ABDOMINAL SEGMENT OF THE LOBSTER. (GEOFFROY.) . 63 



4. IDEAL TYPICAL VERTEBRA. (OWEN.) . . . 102 



5. NATURAL TYPICAL VERTEBRA. (OWEN.) . . .103 



6. .THE ARCHETYPE OF THE VERTEBRATE SKELETON. (OWEN.) 105 



7. IDEAL TRANSVERSE SECTION OF A VERTEBRATE EMBRYO. 



(VON'BAER.) . . . . . . .119 



8. GILL-SLITS OF THE PIG EMBRYO. (RATHKE.) . . 134 



9. MECKEL'S CARTILAGE AND EAR-OSSICLES IN EMBRYO OF 



PIG. (REICHERT.) ...... 145 



10. CRANIAL VERTEBRAE AND VISCERAL ARCHES IN EMBRYO 



OF PIG. (REICHERT.) ..... 148 



u. EMBRYONIC CRANIUM OF THE ADDER. (RATHKE.) . 152 



12. TRANSVERSE SECTION OF CHICK EMBRYO. (REMAK.) . 211 



13. DEVELOPMENT OF THE ASCIDIAN LARVA (KOWALEVSKY.) 272 



14. TRANSVERSE SECTION OF THE WORM NAIS. (SEMPER.) . 280 



15. THE FIVE PRIMARY STAGES OF ONTOGENY. (HAECKEL.). 292 



IX 



