Structure of Small Intestine 194 1. Secretory Apparatus 194 2. Absorbing Apparatus 195 Valvulae Conniventes 196 II. Endgut or Large Intestine 198 II. SERIAL REVIEW OF THE ILEO-COLIC JUNCTION AND CONNECTED STRUCTURES IN VERTEBRATES 200 I. Fishes 200 II. Amphibia 201 III. Reptilia 201 IV. Birds 203 V. Mammalia 204 Monotremata 204 Marsupalia 204 Edentata 206 Sirenia 208 Cetacea 209 Ungulata 209 Rodentia 211 Carnivora 212 Cheiroptera 212 Insectivora 213 Primates 213 III. PHYLOGENY OF THE TYPES OF ILEO-COLIC JUNCTION AND CAECUM IN THE VERTEBRATE SERIES 217 1. Symmetrical Form of Ileo-colic Junction; Mid- and End-gut in Direct Linear Continuity 221 2. Asymmetrical Development of a Single Caecal Pouch, lateral to the Ileo-colic Junction, Mid- and End-gut Preserving their Linear Continuity 223 3. Rectangular Ileo-colic Junction, with Direct Linear Continuity of Caecum and Colon 225 IV. STRUCTURE OF CAECAL APPARATUS AND SPECIALIZED MORPHOLOGICAL CHARACTERS OF COLON IN RODENTS AND UNGULATES 229 1. Caecum Proper 229 2. Structural Modifications of Proximal Segment of Colon analogous in their Functional Significance to the Caecal Apparatus 230 V. CAECAL APPARATUS AND COLON IN HYRAX. 234 PART IV. MORPHOLOGY OF THE HUMAN CAECUM AND VERMIFORM APPENDIX 237 I. Development of the Caecum and Appendix 237