764 J. F. GUDERNATSCH 



tissue,but the main mass of the organ Ues at the second gill branches 

 and here the greatest lateral extension occurs under a transverse 

 muscle. The vertical extension is small and there are no follicles 

 below the aorta. Behind the second gill branches is found the 

 posterior limit of the gland (pi. I, fig. 8). 



The follicles are still smaller than in diaphanus and more 

 uniform in size. The circular type predominates and they are 

 more numerous than in the other species. The colloid is homo- 

 geneous and the follicular epithelium similar to that in diaphanus. 



MENIDIA NOTATA MITCHILL 



Length of specimen 10 cm. The thyreoid mass is rather small 

 (pi. I, fig. 9). The follicles are extremely small, 20-25^, and are 

 scattered along the stem of the aorta between the first and second 

 branchial arteries and out along the second arteries. The lateral 

 extension is greater than the antero-posterior. 



MUGIL CEPHALUS L. 



A mullet 15 cm. long. Small follicles are found in the anterior 

 end of the thyreoid region and are grouped around a vein (fig. 11, 

 A). At the aortic bifurcation the organ is better developed, but 

 is hardly in contact with the gill vessels (fig. 11,5). The thyreoid 

 lies above the aorta, and at the second branchial arteries it comes 

 into contact with the vessel. Here the gland is well developed 

 with numerous large folhcles. The folhcles disappear towards the 

 third aortic branches (pi. I, fig. 13). 



The size of the follicles varies between 30 and 140 m- In section 

 they are slightly oval. In the follicular wall are found transi- 

 tions from flat to high epithelium. The height of the cells varies 

 within the same follicle, showing that it is independent of follicle 

 size. The height of the cells rather depends upon outside pres- 

 sure, e.g., a follicle pressed into oval shape by cartilage shows low 

 epithelium on the longer sides and higher cells on the short sides. 



