258 FRANKLIN P. MALL 



cells responsible for the production of the connective tissue of the 

 endocardium as well as of the valves. Further study will prob- 

 ably show that endothelial connective tissue is by no means of 

 rare occurrence. At any rate it has been definitely settled that 

 the endothelial cells of the liver give rise to the connective tissue 

 of the liver lobule. 



h 







®-y- 



SafSs ar*2 



RCu. 



Fig. 5 Section of the posterior endocardial cushion of an embryo 4.3 mm. long 

 (No. 148). X 360. 



In my study on the development of the connective tissue I 

 was astonished to find in macerated and digested frozen sections 

 that the endothelial tube with its surrounding reticulum can be 

 isolated. 8 In such specimens it is impossible to separate the nuclei 

 from this continuous mass of reticulum ; together they form a syn- 

 cytium. This connection was demonstrated in pig embryos 20 

 mm. long. Although this was entirely out of harmony with the 

 results obtained for other connective tissues, which always arise 

 from the mesenchyme, it had to be accepted and so it was recorded. 



8 Mall, Development of the connective tissues from the connective syncytium 

 Amer. Jour. Anat., vol. 1, 1902, p. 354. 



