THYBEOID GLAND OF THE TELEOSTS 763 



(see General Part). How these corpuscles get into the lumen could 

 not be determined. Erythrocytes are often seen partially im- 

 bedded in the follicular epithelium as if they would force their 

 way in between two cells. In other places corpuscles are found 

 pressed against an epithelial cell which has so flattened out that 

 only a thin layer of cytoplasm separates the corpuscle from the 

 lumen. 



FUNDULUS DIAPHANUS LE SUEUR 



A specimen 9 cm. long. The main mass of the thyreoid is located 

 a little nearer the tip of the tongue than in F. heteroclitus (pi. 

 I, fig. 7) . The posterior end lies at the second branchial arteries 

 where the follicles become scarce and scattered. A further differ- 

 ence from heteroclitus is that the main mass of follicles always lies 

 above the aortic stem, only a few small ones lying below. The 

 lateral extension is here also unimportant. 



The floor of the pharynx is narrow and the connection between 

 it and the ventral musculature is only a narrow streak. In 

 heteroclitus the lateral pharyngeal axis is the longer one, therefore, 

 the lateral thyreoid extension prevails; while in diaphanus the 

 dorso-ventral axis is longer, and here the extension of the thyreoid 

 is mainly in this direction. Ventrally, however, it is prevented by 

 the narrow isthmus, and follicles are mainly found above the aorta 

 (fig. 10, D). In this way the distribution of the follicles may be 

 figured out mechanically in almost every case. 



The follicles are of all sizes, though not so large as in heteroclitus. 

 There are more elliptical or irregular ones and these have a longer 

 axis. The cuboidal cells of the follicular epithelium are not as 

 high as in heteroclitus and cylindrical ones are not found. The 

 colloid is homogeneous and the blood supply is not rich. 



FUNDULUS MAJALIS WALBAUM 



Length of specimen 9 cm. The follicles spread out laterally much 

 further than in the other two species (fig. 10, E, F). They extend 

 for a distance along the first aortic branches. Between the first 

 and second branches there is only a narrow streak of thjTcoid 



