374 B. F. KINGSBURY 



pheral growth of thyreoid cell cords. The vascularization seems 

 to take place rather gradually, being marked in embryos of 32 

 to 40 mm. Lumina (follicular cavities) within the cell cords ap- 

 pear at about this period (32 mm.) and at first contain no demon- 

 strable colloid. In the 40 mm. embryo some of the follicles 

 contain colloid, although not much is present in the oldest em- 

 bryo (48 mm.). At 10 cm. the colloid-containing follicles are 

 numerous. 



Ultimohrancliial body, postbranchial body, or lateral thyreoid 



The writer desires to add nothing to the discussion of this 

 structure already pubhshed (Kingsbuiy 14 b). The view then 

 taken was that this derivative gives no good evidence of being 

 a 'vestigial gland,' which in lower forms possesses a duct opening 

 into branchial pouch or pharynx. Its origin, form and fate appear 

 to be due to a persistence of a growth tendency in the branchial 

 epithehum, as molded by the attending growth conditions 

 and movements, but without any characteristics that mark it 

 out as an 'organ'- — of past or present usefulness- — or as an ex- 

 ternally or internally secreting gland. Its fate appears to be a 

 degeneration within the thyreoid, although it must be confessed 

 that this has not yet been definitely proved. 



ENDOCRINE ORGANS 



In view of the ver}^ large amount of work, experimental and 

 observational, being done at the present time on the endocrine 

 organs, by both the physiologists and clinicians, it may seem 

 somewhat presumptuous for a morphologist to venture upon 

 a discussion of their interpretation and significance, particularly 

 as discordant evidence indicates — as has been insisted on by 

 others^ — that the time is not yet ripe and a much greater body 

 of facts must be accumulated before broad interpretations may 

 be drawn. The embryologist cannot escape, however, a consider- 

 ation of certain aspects of the problem; what an organ becomes 

 is a function of its origin and development, and its activity in 

 the adult is determined by its origin and ancestral history. 



