ORIGIN OF BLOOD AND ENDOTHELIUM 9 



During the last few years, special attention has been 

 devoted to the study of these embryos without a circulation 

 of their body fluids with the main object of analyzing as com- 

 pletely as possible, the origin and subsequent development of 

 the heart, vessels and blood. All of the experiments have been 

 repeated through three summers in the Marine Biological Labora- 

 tor}'^ at Woods Hole. It has been possible to produce embryos 

 that were almost normal in all particulars yet in which the blood 

 failed to circulate on account of the fact that the heart was 

 blind at one or both ends or disconnected at the venous end or 

 finally was a completely solid cord of tissue. 



The embryos were studied in life and the particular indi- 

 viduals which had been so observed were fixed and finally studied 

 in microscopic sections. The observations made on the experi- 

 mental embryos have in all instances been completely checked 

 and controlled by careful detailed study of the blood and vessels 

 in normal embryos. 



The experiments have been performed on two species of Fundu- 

 lus, heterocHtus and majalis, and the results are practically identi- 

 cal for both. The eggs were stripped from the female into small 

 dishes containing no water and fertilized by milt pressed from 

 the male. About fifteen minutes after the application of the 

 sperm water was added to the eggs. In this way one gets a very 

 high percentage of fertiUzed eggs, while fertilizing the eggs under 

 water or adding sperm to a dish of water gives a much poorer 

 result. The fertilized eggs are then divided into groups so that 

 the experiment and control are all from similar sources. The 

 eggs just before dividing into the two-cell stage were introduced 

 into solutions of alcohol. 



The solutions which gave the most favorable results were pre- 

 pared in the following way: 50 cc. of sea-water was placed in 

 each dish and to this was added respectively, 1.5 cc, 2 cc. 2.3 

 cc, 2.6 cc, 2.8 cc, 3 cc, 3.5 cc, of 95 per cent commercial alco- 

 hol. The eggs remained in these solutions for twenty-four hours, 

 after which time the solution was renewed. After forty-eight 

 hours the eggs were removed from the alcohol solutions and 

 placed in pure sea-water. 



