280 SANTE NACCARATI 



Other researches were conducted by Wolfer ('80), Stieda ('81), 

 Dohrn ('87), Gotte ('75), DeMeuron ('86), Maurer ('85), Balfour 

 ('78), Kastschenko ('87), Piersol ('88), Prenant ('94-'99), 

 Van Bemmelen ('85-' 93), Piatt ('96), Simon, SouUe ('97), 

 Verdun, Jacoby ('94, '96, '97), Verson ('07), and others more 

 recently, too many to be quoted here, with resulting confirmation 

 of the origin of the thyreoid from three distinct and originally 

 independent rudiments, i.e., one middle and two lateral thyreoid 

 rudiments, in mammals. 



According to Maurer ('99) Echidna, and according to SjTning- 

 ton ('97, '98) the Edentata and Marsupialia are exceptions to 

 this rule, in that they retain the independence, of the three 

 rudiments, having, in addition to a two-lobed thyreoid, two 

 organs developed from 'the lateral rudiments, homodynamic 

 with the postbranchial or suprapericardial bodies, by which 

 name they are called. 



Livini ('02) made a careful study of the embryology of the 

 organs of the thjmius-thyreoid system in Amphibia urodela, and 

 found the thyreoid arises as a single medial solid epithelial 

 bud from the caudal wall of an entodermic spur of the pharyn- 

 geal floor which enters in intimate contact with the ecto- 

 derm. He considers this spur as a rudiment of the hypobranchial 

 groove of the Tunicata. However, the level at which the thyreoid 

 arises cannot be established because when its bud is already 

 recognizable, neither the branchial pouches nor the cartilages 

 of the branchial arches have yet been differentiated. 



NOTES ON THE COMPARATIVE ANATOMY OF THE THYREOID 



Cyclostomata. In the lamprey the thyreoid gland is but 

 little developed in the adult. In the larvae (Ammocoetes) 

 it remains in open communication with the buccal cavity, at a 

 level between the third and the fourth branchial slit, in such a 

 manner that it may be considered as a diverticulum of the 

 ventral wall of the pharynx. With the coming of the meta- 

 morphosis it becomes a glandular organ of vesicular structure 

 and is isolated from the pharynx. The arrangement in the 

 larvae recalls a homologous relation between the thyreoid in the 



