8 CHARLES R. STOCKARD 



hearts or of remnants of the heart which remained after the 

 operation. The embryos were not particularly adapted for the 

 study of the blood questions since some circulation always took 

 place, and this no doubt was sufficient to contaminate the orig- 

 inal sources of blood cells and so confuse the situation. Loeb 

 ('12) has reported experiments on bony fish hybrids and embr^^os 

 treated with certain chemicals in which there was a heart beat 

 but no circulation. These embryos were, however, not studied 

 for either blood or vascular genesis. 



The first demonstration of the fact that the embryo could 

 develop without the circulation of the blood was given by Loeb 

 in 1893. He showed that Fundulus eggs developing in solu- 

 tions of KCl had no heart beat and no circulation of the blood, 

 yet some vessels formed. In 1906 the wTiter repeated this 

 experiment and confirmed Loeb's results entirely, but found 

 that the vascular system and general development of the embryo 

 was extremely abnormal and was hardly reliable for conclusive 

 studies on the origin of special tissues. 



With these experiments in mind, and appreciating the prob- 

 lems indicated above regarding the origin of blood as weU as vas- 

 cular endotheliimi, I have undertaken an extensive experimental 

 analysis of this subject in conjunction wdth a careful systematic 

 study of the histogenesis of the blood and vessels in normal 

 embryos. The results of the experimental study which has been 

 carefully followed during the past three years are presented in 

 the following pages of this paper. 



METHODS OF EXPERIMENT AND MATERIAL 



Six years ago, while studying the influence of alcohol and 

 various anaesthetics on the development of Fundalus embryos, 

 I noticed that many of these embryos had a feeble heart beat, 

 but no circulation of the blood. At that time, particular 

 attention was given to a study of the defects of the central 

 nervous system and of the organs of special sense and no attempt 

 was made to investigate thoroughly the conditions present in 

 other tissues and organs of the body. 



