482 J. A. BADERTSCHER 



Cells of a peculiar type (fig. 7, k). are quite frequently found 

 among lymphocytes and eosinophile cells in the thymic septa. 

 They are derived from large lymiDhocytes and are characterized 

 by a part of or the entire superficial layer of the basophilic cyto- 

 plasm staining a deep red similar to the erythrocytes or the 

 granules in eosinophile cells. Their nuclei have the character- 

 istic structure of those in the lymphocytes or eosinophile cells. 

 They cannot, therefore, be erythroblasts which have granular 

 nuclei but must be classed with the eosinophile cells. The 

 cells of this type are never very numerous and the youngest 

 stage in which they, were found was in the body mesenchyme 

 of a 25 mm. embryo. They occur most frequently in the thymic 

 septa of quite late developmental stages. 



The origin of the eosinophile cells in the lobules of the thymus 

 can now be discussed briefly. Their structure is the same as 

 of those in the interlobular septa. They belong to the mono- 

 nuclear type. They were first found in the lobules of the thy- 

 mus of a 42 mm. embryo. In this stage they are very rare and 

 can be found only after prolonged searching. Their number 

 increases in successively advanced developmental stages. In 

 the 125 mm. embryo they are readily found m both the cortex 

 and medulla. In the 180 mm. embryo a group of them was 

 found in the medulla of the mid-cervical segment while those 

 lying singly are more numerous than in younger stages. In 

 the full term fetus they are present in appreciably greater num- 

 bers than in the previous stage, groups of them being found 

 in both the cortex and medulla and many can be found lying 

 singly. Since the red blood-cells were considered particularly 

 in the superficial thymus of a 270 mm. (full term) fetus the eosino- 

 phile cells also in that region will be emphasized. Some groups 

 of eosinophile cells are found in the immediate vicinity of blood 

 vessels but as many are found that are not associated with the 

 vessels. The groups occur most frequently along the border 

 of or near the vicinity of groups of erythrocytes but some groups 

 are isolated and as far as position is cfoncerned their origin does 

 not seem to bear any relation to erythrocytes. Here as in the 

 interlobular septa the origin of some is, undoubtedly, from the 



