EXPLANATION OF PLATES I TO III 



Plates I and II show the regions of distribution of the thyreoid elements in 

 different species. I, aortic bifurcation or first branchial arteries; II, III and IV, 

 the second, third and fourth branchial arteries. 



1 

 2 

 3 

 4 

 5 

 6 



9 

 10 

 11 

 12 

 13 



Anguilla chrysypa 

 Clupea harengus 

 Brevoortia tyrannus 

 Osmerus mordax 

 Siphostoma fuscum 

 Fundulus heteroclitus 

 Fundulus diaphanus 

 Fundulus majalis 

 Menidia notata 

 Sarda sarda 

 Pomatomus saltatrix 

 Morone americana 

 Mugil cephalus 



Stenotomus chrysops 

 Micropogon undulatus 

 Tautogolabrus adspersus 

 Tautoga onitis 

 Opsanus tau 

 Muraenoides gunellus 

 Oncorhynchus kisutch 

 Salmo mykiss 

 Salmo irideus, age 1 month 

 Salmo irideus, age 1 year 

 Cristivomer namaycush 



Plate III, Diagrams of actual portions of the thyreoid gland visible to the 

 naked eye. 



28 and 29 Salvelinus fontinalis 



30 and 31 Pseudopleuronectes americanus 



32-41. Ten specimens of Cynoscion regalis, demonstrating the great variability 

 in extent and position of the organ within the species. 



