280 GEO. A. THIEL AND HAL DOWNEY 



sia in the spleen of the adult; 9) development of the splenic fol- 

 licles in postnatal animals. 



The investigators who have studied the problem of splenic 

 development can be placed in two distinct groups. The first 

 maintains that the spleen is of mesodermal origin ; the second that 

 the organ owes its development to cells that are given off from 

 the endoderm. The first class of workers may be further di- 

 vided into those who hold that the rudiment of the organ is 

 limited to a differentiation of the mesenchyme, and into those 

 who maintain that the peritoneal epithelium also plays a part in 

 the first stages of development. 



The chief exponents of the endodermal theory are Schenk, 

 Gotte, Maurer, v. Kupffer, Woit, and Glas. Thase men, with 

 the exception of Maurer and Gotte, believed there was a definite 

 relation between the embryonic spleen and pancreas, and conse- 

 quently considered the spleen as being dependent upon the 

 endodermal cells which are given off from the primitive diverticu- 

 Imn of the pancreas. The work of Maurer stands alone in main- 

 taining a relation between the endodermal epithelium of the 

 intestinal tract and the splenic rudiment. According to Gotte, 

 the splenic rudunent of the toad is composed of a mass of free 

 'Dotterbildungszellen' — primitive blood-cells derived from the 

 yolk endoderm and forced into the mesenchyme by the heart beat. 



Choronshitzky beUeved that free cells from the intestinal 

 epithelium may enter the mesenchyme and become transformed 

 into mesenchymal tissue, and that therefore the endodermal ele- 

 ments are concerned only to the extent that they are functional 

 in the production of the accumulation of mesenchyme for the 

 splenic rudiment. 



Radford has made a careful study with special reference to 

 Maurer's conclusions, but failed to find sufficient evidence to 

 corroborate his views. Kraatz, Tonkoff, and Nicolas also report 

 the absence of cells from the digestive tract. 



The group of investigators that maintains a mesodermal splenic 

 rudiment is represented by Miiller, Koelliker, Laguesse, Minot, 

 Pinto, Toldt, Janosik, Tonkoff, Choronshitzky, Mietens, and 

 Danchakoff. Of this group Choronshitzky, Tonkoff, Miiller, and 



