114 CARNEGIE INSTITUTION OF AVASHINGTON. 



chick. Her findings, briefly stated, are as follows: The primary- 

 superficial IjTnphatics of chick embryos form a rapidly growing, 

 frequently anastomosing, capillary network. This primitive plexus 

 maintains numerous open connections with the venous system in 

 certain places. For over 24 hours the pressure in these earliest lym- 

 l^hatics remains less than the side-pressure in the connecting veins 

 and, consequently, there is no lymph-flow in the early plexus. Instead, 

 it contains blood, which backs up into it from the communicating 

 veins. The pressure of the fluid in the lymphatics gradually increases 

 and finally overcomes that of the veins. The first lymph-flow which is 

 then established is feeble and easily disturbed. The lymph-flow 

 gradually becomes more rapid and steady, but its course is readily 

 altered b}'- various mechanical factors. A day later the pressure in the 

 superficial lymphatics has increased still more and, for various reasons, 

 the outflow into the veins is interfered with. At certain points two 

 conflicting pressures are present, and here the lymph-flow becomes 

 sluggish. The endothelium of these early lymphatics responds to the 

 passage of fluid over its interior by the differentiation of definite ducts 

 or channels out of the indifferent primitive network. With the 

 increased flow of lymph these channels enlarge and others are formed. 

 That the formation of such channels is due to the lymph-flow and to 

 mechanical factors, rather than to arbitrary predetermination, is 

 e\'ident from the frequent variations which occur in the position of the 

 main ducts in chicks of the same stage. The endothelial wall of the 

 early IjTnphatics also responds to the increased pressure, caused by 

 interference with the lymph-flow and the damming back of fluid, by 

 expanding to form sac-like enlargements. The size which these 

 sacs may attain is influenced to some extent by the looseness of the 

 surrounding tissue. 



Professor Franz Keibel, our Research Associate, has made a new 

 report upon early implantation. To detennine the line of demarcation 

 between maternal and embryonal structures he employed Bielschow- 

 sky's method, with which the connective-tissue fibrils are stained 

 intensely black, so that (as they are numerous in the nmcous mem- 

 brane of the uterus) it is quite easy to separate the two kinds of struc- 

 tures. In a specimen about 3 weeks old it is found that the individual 

 trophoblast cells are in advance in implantation and where they come 

 in contact with the connective-tissue fibrils the latter swell and dis- 

 integrate. At this stage of development the trophoblast cells do not 

 intenningle with the decidua cells. The epithelial cells of the glands 

 and the endothelial cells lining the blood-vessels degenerate and disap- 

 pear in front of the advancing trophoblast. The line of separation is 

 well-marked bj'^ the presence of connective tissue on the maternal side 

 and by its absence on the embryonal side. From this study it would 

 appear that the syncytium prevents the maternal blood from coagulat- 



