A STUDY OF WANDERING MESENCHYMAL CELLS 

 ON THE LIVING YOLK-SAC AND THEIR DEVELOP- 

 MENTAL PRODUCTS: CHROMATOPHORES, VAS- 

 CULAR ENDOTHELIUM AND BLOOD CELLS^ 



CHARLES R. STOCKARD 



Department of Anatotny, Cornell University Medical College, New York City 



THIRTY-FIVE TEXT-FIGURES 



I. Introduction 525 



II. Material and methods of study 528 



III. The early wandering cells 530 



IV. Development and differentiation of the wandering cells 540 



1. Chromatophores 540 



a. The black type chromatophore 540 



b. The brown type chromatophore 544 



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



culation of the blood 547 



d. Relationship of chromatophores to blood and endothelial 



cells. 551 



2. History of the endothelial cells 552 



3. Blood corpuscles on the yolk-sac of teleost embryos 565 



V. Discussion and conclusions 581 



VI. Summary 589 



Literature cited 594 



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 The present contribution is a continuation of the author's study of "The 

 origin of blood and vascular endothelium in embryos without a circulation of the 

 blood and in the normal embryo" which appeared in the September number of 

 this journal. This first part is referred to in the following pages as 'the previous 

 paper.' 



525 



THE .4.MERIC.\N JOURNAL OF ANATOMY, VOL. 18, NO. 3 

 NOVEMBER, 1915 



