DEVELOPMENT OF THE ADRENALS IN THE TURTLE 83 



comes comparatively shorter and the glands gradually assume the 

 general form and location which they maintain during adult life. 

 In embryos twenty-five days old, the adrenals are still closely 

 associated with the anlagen of the prevertebral sympathetic 

 plexuses and a few cells apparently continue to advance from the 

 latter into the masses of cells of sympathetic origin which are 

 becoming approximated more and more closely to the cortical 

 substance. In the anterior region, the right and the left adrenal 

 are distinct and are located approximately at the level of the 

 coeliac plexus which lies between them. Farther posteriorly the 

 right and the left adrenal lie in contact with each other and are 

 apparently connected by a broad bridge of cortical cells; the 

 principal mass of the prevertebral plexuses being embraced in the 

 angle between them (fig. 7, ad). Numerous aggregates of cells 

 of sympathetic origin lie in close contact with the cortical sub- 

 stance (fig. 7, cc). These aggregates are most conspicuous at the 

 dorsal and the mesial aspects of the adrenals, but aggregates of 

 considerable size may be observed surrounding the entire mass of 

 the cortical substance. The cells of the cortical substance are 

 becoming arranged into more or less distinct aggregates with 

 numerous vascular spaces appearing between them. Not infre- 

 quently the aggregates of cells of sympathetic origin penetrate 

 deeply into these vascular spaces, while in sections occasionally 

 such cell-groups occur completely surrounded by the cortical 

 substance. 



After the twenty-fifth day of incubation, the association of the 

 cortical and the chromaffin substance becomes more intimate. 

 In embryos from thirty to thirty-six days old, the masses of cells 

 of sympathetic origin have become more conspicuous than in the 

 earlier stages and penetrate more deeply into the spaces between 

 the aggregates of the cortical cells (fig. 8, cc) . Groups of cells of 

 sympathetic origin which in sections appear to be completely sur- 

 rounded by the cortical substance are now scattered irregularly 

 throughout the entire section. Such areas in the section probably 

 do not represent groups of cells which have become completely 

 separated from the masses of cells of sympathetic origin aggrega- 

 ted at the surface of the cortical substance, but are, doubtless, 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 13, NO. 1 



