■37- 



TTie Tl^yrold and Salivary niands In the Adult Lamprey, 



The condition of the thyroid in the adult lamprey 

 was studied in several large sea lampreys (P. marinus) taken 

 at the herring fisheries of the Susquehanna River, and in a couple 

 of "brook lampreys (P. branchialis) from Ithaca, II. Y. 



Wilhelm Muller says (Jenaische Zeitschrift, Ed. VII) 

 that the thyroid, in the"sexually mature" animal, extends under- 

 neath the long tongue muscle from the 2nd to the 4th gill sac, 

 and is built up of a number of closed follicles lined with in- 

 tensely brown-yellow epithelium. Me says it cannot be mistaken 

 for the salivary gland, lying under the eye and opening by a 

 duct into the mouth. 



A study of serial sections of a couple of recently 

 transformed brook lampreys confirmed Muller 's description of the 

 position and anatomy of the adult thyroid, but careful dissection 

 of one or two adult sea lampreys and even sections of part of the 

 floor of the pharynx failed to show any trace of the thyroid. 

 As the brook lampreys were, as has been said, only just trans- 

 formed, while the sea lampreys were killed at sexual maturity, 

 it is possible that the thyroid, which is ductless and a mere 

 rudiment in any case, had nearly or (julte disappeared in the 

 older animals. As is seen in Fig. 10 a, the thyroid, which in 

 the younger larval stages was enormously large, proportionally. 



