DEVELOPMENT OF THE THYMUS 467 



the course of blood vessels to the outer tunic of which many 

 were attached. He derived them all from connective tissue 

 cells. 



Schaffer ('91) apparently was the first investigator to observe 

 eosinophile cells in the thymus. In various developmental 

 stages of the human thymus he found large numbers of eosino- 

 phile cells in the connective tissue surrounding the thymus, in 

 the interlobular septa, and along the course of some of the cap- 

 illaries in the medulla. A few also were found in the cortex. 

 The size of the granules vary and the nucleus he described as 

 being round. His investigations of the eosinophile cells in 

 the thymus were then too incomplete to say anything definitely 

 regarding their origin but he believed that they were not identi- 

 cal with the Agranular cells' of Watney. In the medulla of 

 the involuting thymus of the mouse he ('09) found many eosino- 

 phile cells and numerous free granules that stained intensely 

 with eosin. These granules he regarded as products of degen- 

 erated epithelial cells. Within the lobules and in the inter- 

 lobular septa of the involuting thymus many plasma cells were 

 also present. These he derived from the small lymphocytes 

 of the thymus. Many had the appearance of undergoing de- 

 generation. 



Goodall ('05) is of the opinion that the pseudo-eosinophile 

 cells in the region of Hassall's corpuscles in the thymus of the 

 guinea-pig, are derived from the blood. 



Maximow ('09) claims that different types of granular cells 

 were found in the thymus in different species of mammals. In 

 the more advanced stages of rabbit embryos an appreciable 

 number of pseudo-eosinophile myelocytes were found in the 

 interlobular septa,- cortex and medulla. Only a few mast cells 

 were found, most of which were in the septa. In guinea-pig 

 embryos psuedo-eosinophile myelocytes were seldom found. 

 In cat embryos 35 to 50 mm. in length special myelocytes and 

 leucocytes were found in quite large numbers, while in embryos 

 120 to 130 mm. long numerous mast cells were found in the deeper 

 portions of the cortex and in the medulla. In the septa they 

 were less numerous. Only an occasional eosinophile cell was 



