GERMINATING ENDOTHELIUM. 5 



deduced from the fact that besides the appearances of constriction 

 and division of the polyhedral or club-shaped endothelial cells, there 

 are always numbers of smaller spherical lymphoid elements to be 

 found amongst them, which are detached from the surface, that is to 

 say, which have become perfectly separated. 



(Terminating endothelium is to be found just as richly on the 

 omentum of the dog, especially in the non-fenestrated portion, where 

 it is to be met with in the form of isolated smaller or larger groups. 



The pleura mediastini of dogs, cats and monkeys is a very good 

 object for studying germinating endothelium. On the trabeculae of 

 that membrane, as well as on the complicated system of tracts which 

 extends freely over the surface, there exist numbers of lateral or inter- 

 calated nodular swellings of various size, the surface of which is 

 covered abundantly with young endothelium. From the great number 

 of club-shaped and pedunculated two-nucleated endothelial cells, and 

 from the number of spherical cells which are more or less loosely 

 attached to the surface of the above-mentioned swellings, we cannot 

 but deduce that there is going on a very abundant production of lym- 

 phoid cells. 



Not less instructive is the mesogastrium of the frog. If this 

 membrane of a female frog during the winter months is examined in 

 an indifferent fluid or after staining with silver solution, one recog- 

 nises on the surface of the dense portion, especially on the trabeculae 

 of the fenestrated portion, numbers of places where the endothelium 

 possesses the germinating character : they appear either in small 

 groups or as nodules which project freely on the surface of the trabe- 

 culoe. 



This germinating endothelium, which is similar to that described 

 in mammals as regards its substance, shape, and nucleus, possesses the 

 peculiarity that the surface of the endothelial cells is provided with a 

 bunch of cilia. If the membrane is mounted in serum, and the cover 

 glass supported by small strips of paper, the ciliary movement can be 

 observed during three hours and more with equal rapidity. The pro- 

 liferation of this ciliated endothelial cells takes place in the following 

 way : one finds not rarely a ciliated cell of a columnar shape which 

 possesses two nuclei, situated above each other in the longitudinal axis 



