716 J. F. GUDERNATSCH 



into the musculus sternohyoideus, the folHcles follow in the course 

 and are thus distributed far ventrally within the muscle. The 

 nuynber of folUcles along the sides of the aorta is always less than 

 either above or below it. Thisl y no means contradicts the state- 

 ment made above that the lateral extension of folHcles outweighs 

 the dorso-ventral one. Only in the genus Fundulus, especially 

 in majahs, less so in heterochtus, where a transverse inter- 

 branchial nmscle pushes the vessels away from the skeletal parts, 

 is the dorsal extension small, or sometimes lacking entirely. Here 

 the follicles extend directly away from the aorta towards the 

 bases of the gills. 



Along the aortic stem between the bases of the gill arteries 

 the lateral extension is somewhat limited and reaches its height 

 along the branchial arteries. The vessels seem to serve as bases 

 along which the follicles migrate. The free space about the gill 

 arteries becomes narrower and narrower as the gill arches are 

 approached and therefore the number and size of the follicles 

 decrease towards these points until there is no more room for 

 extension. When, however, there exists an especially open passage 

 along the vessels the foUiclcs may even extend into ^^ gill arches, 

 to a considerable distance beyond the point of their og-igin. Such 

 cases are common in trout (text fig. ID). 



The peculiar distribution of the thyreoid elements forces us 

 to regard the organ in bony fishes as unpaired, a view also sup- 

 ported by embryology. This statement should be especially 

 emphasized, as in Wiedersheim's Comparative Anatomy, 1907, 

 the author still speaks of the thyreoid gland in the Teleosts as a 

 paired organ, although Maurer in 1886 (p. 134) criticizes this 

 statement in an earlier edition. On another page, (p. 140) Maurer 

 himself claims that the main bulk of the organ at a certain stage 

 is not paired, while later single portions of the gland lying in the 

 median line, as well as on both sides of the truncus arteriosus, 

 take a paired arrangement. This is certainly incorrect, since the 

 follicle groups on the sides of the aorta are not only unpaired but 

 are also not bilaterally arranged. 



The relationship between the thyreoid gland and the stem of the 

 ventral aorta is purely anatomical and without any physiological 



