DEVELOPMENT OF THE THYMUS 481 



enough to account for all of the granules in the numerous eosino- 

 phile cells even though all should be ingested by lymphocytes. 

 However, lymphocytes with only a few granules in their cyto- 

 plasm and lying among free eosinophile granules suggests that 

 some eosinophile cells are simply lymphocytes ingested with 

 debris of degenerated erythrocytes. This view of the origin 

 of the granules in eosinophile cells is held by Weidenreich ('08, 

 '08, mammals), and by Badertscher ('13, amphibia) in a some- 

 what modified form in that some of the granules are also formed 

 from the debris of degenerated muscle tissue. Also circumstan- 

 tial evidence indicating the formation of eosinophile granules 

 from erythrocytes is not wanting and may be enumerated as 

 follows: (1) The free red blood-cells appear in the interlobular 

 septa in advance of eosinophile cells; (2) The red blood-cells 

 appear in large numbers in earlier developmental stages than 

 do large numbers of eosinophile cells, e.g., in the septa of the 

 thymus of a 125 mm. embryo the red blood-cells are more numer- 

 ous than in any other developmental stage while the largest 

 number of eosinophile cells occur in the septa of the thymus 

 of a 165 mm. fetus; (3) As the free red blood-cells in the septa 

 of late stages begin to decrease in number the eosinophile cells 

 decrease in number in correspondingly later stages, e.g., the 

 red blood-cells in the thymic septa of 165 and 180 mm. fetuses 

 are not as numerous as in the 125 mm. embryo but the eosino- 

 phile cells in the 270 mm. embryo are less numerous than in 

 the 165 and 180 mm. fetuses. These facts can be stated in a 

 general way by saying that the height and decrease of erythro- 

 cyte formation in the septa are followed respectively by the 

 height and decrease of eosinophile cell formation in somewhat 

 later stages. If the granules in eosinophile cells are products 

 of degenerated erythrocytes this apparent relationship exist- 

 ing between these two types of cells can be accounted for only 

 on the assumption that the majority of free red cells in the septa 

 undergo dissolution and the products of degeneration taken up 

 by the lymphocytes, possibly in soluble form, and in them 

 transformed into granules. 



