150 JEREMIAH S. FERGUSON 



only with difficulty and not frequently when the needle is thrust 

 into the substance of the gland. 



Balfour ('81) referring to the development of the organ in Scyl- 

 lium and Torpedo says that at first it is solid and attached to the 

 esophagus. "Eventually its connection with the throat becomes 

 lost, and the lobules develop a lumen." 



Dohrn ('84) in his plate XI, fig. 5, indicates by outline the thy- 

 roid gland of Ammocetes, but does not illustrate or describe the 

 thyroid gland of the Selachii, though in his text he includes an 

 extended description of the thymus of the latter animals. His 

 outline of the thyroid of Ammocetes does not conform to that the 

 the gland in the Selachii. 



De Meuron ('86) says that in Scyllium the thj'^roid is elongated, 

 in Galeus and Acanthias, much flattened, in Raia pyramidal or 

 rounded. It lies just above the terminal bifurcation of the bran- 

 chial artery. In Myelobates it lies behind the os hyoideus, 

 beneath the sterno-mandibularis muscle, and is triangular in 

 shape, short, flattened, transversely elongated, and has a length of 

 2 cm. In Acanthias the thyroid gland presents an irregular con- 

 tour, certain groups of follicles being even completely detached, 

 and placed around the principal group. The observations of De 

 Meuron would appear to be accurate as far as they go but are 

 possibly founded upon the examination of too few individuals. 

 Thus in Squalus acanthias I found the thyroid frequently broken 

 as described by De Meuron for Acanthias but other individuals 

 presented a thyroid which was perfect, not the least broken up 

 or irregular in contour, and in the closely related ^Nlustelus canis 

 irregularity of contour is certainly the exception, not the rule. In 

 Scyllium he says the thyroid is elongated and I find that superfi- 

 cial examination of the related species Carcharias, would indicate a 

 similar condition, but if the semi-opaque white mass of connective 

 tissue, in which the thyroid gland of Carcharias is heavily clothed 

 and so closely invested that it seems to form paart of the gland, 

 be dissected out and held, stretched in its normal form, between 

 the bright sun and the eye of the observer there is readily seen 

 within the reddish-white connective tissue mass the outline of the 

 yellowish-orange thyroid gland, which instead of having theelon- 



