PART 2 



CONTENTS 



I. Introduction 105 



II. Material and methods of study 108 



III. The early wandering cells 110 



IV. Development and differentiation of the wandering cells 120 



1. Chromatophores 120 



a. The black type chromatophore 120 



b. The brown type chromatophore 124 



c. Behavior of the chromatophores in specimens with no cir- 



culation of the blood 127 



d. Relationship of chromatophores to blood and endothelial 



cells 131 



2. History of the endothelial cells 132 



3. Blood corpuscles on the yolk-sac of teleost embryos 145 



V. Discussion and conclusions 161 



VI. Summary 169 



Literature cited. . . 174 



INTRODUCTION 



The aim of the present consideration is an analysis of the 

 histogenetic changes passed through by the mesenchymal cells 

 in the living yolk-sac. A study of the origin and development 

 of the blood and vascular endothelium in normal teleost embryos, 

 and in other specimens in which the circulation of the blood had 

 been experimentally prevented, made it evident that a detailed 



1 This second part of the Memoir is a continuation and expansion of the 

 foregoing study on "The origin of blood and vascular endothelium in embryos 

 without a circulation of the blood and in the normal embryo." The first part 

 is referred to in the following pages as the 'previous paper.' 



105 



