290 GEO. A. THIEL AND HAL DOWNEY 



From these gleanings of the hterature we see that most inves- 

 tigators report an open circulation through the splenic pulp. 

 The work of Helly stands out alone as a last defense of a closed 

 system. The conclusions of some of the earlier workers are far 

 from convincing, for, as has been pointed out by Von W. Schulte, 

 "while the results of injection demonstrate the permeability of 

 the vessel wall, as do in life the passage of cells and fluids, they 

 do not afford us the opportunity of ascertaining the structure of 

 the wall or the nature of the orifices." 



2. Circulation of the early embryonic spleen and the development 

 of the venous sinuses 



The vascularization of the early embryonic spleen has been 

 given but sUght attention. It has been superficially investi- 

 gated by Rathke (in amphibians), Remak (in birds), Arnold, 

 Bischoff and KoUiker (in mammals), and merely mentioned by 

 many others, Peremeschko and Mliller held that the spleen was 

 supplied with vessels from the very earliest stages, and Radford 

 also adds that it soon becomes very vascular. KoUiker, however, 

 holds that the vessels do not appear until toward the end of 

 embryonic life. The presence of spaces in the splenic mesenchyme 

 is mentioned by Choronshitzky in his work on the chick and on 

 various mammalian forms. He states that the vena lienaUs is 

 present before the splenic rudiment is established. Its branches 

 penetrate the rudmient and lose their endothelium. In the rudi- 

 ment the veins are merely clefts in the mesenchyme which are 

 in communication with the intercellular spaces of the latter. 

 The embryonic cells can therefore enter the lumina where they 

 become transformed into blood-cells. The splenic artery has no 

 relation to the early rudiment, but grows in later. Toldt and 

 Tonkoff also find blood-vessels with indistinct walls in the early 

 rudiment. According to Laguesse, the first vessels of the spleen 

 are merely lacunae in the mesenchyme which connect with 

 branches of the subintestinal vein (in fishes). Daiber's studies 

 on the salamander also reveal the presence of lacunae in the very 

 young spleen, but she sees no distinct endothehum at their bor- 

 ders. These lacunae may contain two or three early blood- 



