2io TABLE OF CONTENTS. 



CHAPTER V. 



STAGES B G, pp. 298 314. 



General features of the epiblast, Original uniform constitution. Separation into 

 lateral and central portions. The medullary groove. Its conversion into the me- 

 dullary canal. The mesoblast. Its division into somatic and splanchnic layers. 

 Formation of protovertebrce. The lateral plates. The caudal swellings. The 

 formation of the body-cavity in the head. The alimentary canal. Its primitive 

 constitution. The anus of Rusconi. Floor formed by yolk. Formation of cellular 

 floor from cells formed around nuclei of the yolk. Communication behind of neural 

 and alimentary canals. Its discovery by Kowalevsky. Its occurrence in other 

 instances. General features of the hypoblast. The notochord. Its formation as a 

 median thickening of the hypoblast. Possible interpretations to be put on this. 

 Its occurrence in other instances. 



CHAPTER VI. 



DEVELOPMENT OF THE TRUNK DURING STAGES G TO K, pp. 315 360. 



Order of treatment. External epiblast. Characters of epiblast. Its late division 

 into horny and epidermic layers. Comparison of with Amphibian epiblast. The 

 unpaired fats. The paired fins. Their formation as lateral ridges of epiblast. 

 Hypothesis that the limbs are remnants of continuous lateral fins. Mesoblast. Con- 

 stitution of lateral plates of mesoblast. Their splanchnic and somatic layers. 

 Body-cavity constituting space between them. Their division into lateral and ver- 

 tebral plates. Continuation of body-cavity into vertebral plates. Protovertebrae. 

 Division into muscle-plates and vertebral bodies. Development of muscle-plates. 

 Disappearance of segmentation in tissue to form vertebral bodies. Body-cavity 

 and parietal plates. Primitive independent halves of body-cavity. Their ventral 

 fusion. Separation of anterior part of body-cavity as pericardial cavity. Com- 

 munication of pericardial and peritoneal cavities. Somatopleure and splanchnopleure. 

 Resume. General considerations on development of mesoblast. Probability of 

 lateral plates of mesoblast in Elasmobranchs representing alimentary diverticula. 

 Meaning of secondary segmentation of vertebral column. The urinogenital system. 

 Development of segmental duct and segmental tubes as solid bodies. Formation of a 

 lumen in them, and their opening into body-cavity. Comparison of segmental duct 

 and segmental tubes. Primitive ova. Their position. Their structure. The noto- 

 chord. The formation of its sheath. The changes in its cells. 



CHAPTER VII. 



GENERAL DEVELOPMENT OF THE TRUNK FROM STAGE K TO THE 

 CLOSE OF EMBRYONIC LIFE, pp. 361 377. 



External epiblast. -Division into separate layers. Placoid scales. Formation 

 of their enamel. Lateral line. Previous investigations. Distinctness of lateral line 

 and lateral nerve. Lateral nerve a branch of vagus. Lateral line a thickening of 

 epiblast. Its greater width behind. Its conversion into a canal by its cells assuming 

 a tubular arrangement. The formation of its segmental apertures. Mucous canals 

 of the head. Their nerve-supply. Reasons for dissenting from Semper's and Gotte's 

 view of lateral nerve. Muscle-plates. Their growth. Conversion of both layers into 



