106 PROCEEDINGS OF THE ACADEMY OF [Feb., 



the lateral cell-groups have not taken part in the coil, instead of 

 projecting as they do for a considerable distance posterior to the coil. 



The Thyroid and Salivary Glands in the Adult Lamprey. 



The condition of the thyroid in the adult lamprey was studied in 

 several large sea lampreys (Petromyzon marinus) taken at the her- 

 ring fisheries of the Susquehanna river, and in a couple of brook 

 lampreys (P. branchialis) fi'om Ithaca, N. Y. 



Willielm Miiller says' that the thyroid in the " sexually mature " 

 animal extends underneath the long tongue muscle from the second 

 to the fourth gill-sac, and is built up of a nvimber of closed follicles 

 lined with intensely brown -yellow epithelium. He says it cannot 

 be mistaken for the salivary gland, lying under the eye and open- 

 ing by a duct into the mouth. 



A study of serial sections of a couple of recently transformed 

 brook lampreys confirmed Miiller' 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 transformed, 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 quite disappeared in the older animals. As is seen in fig. 

 lOffl, the thyroid, which in the younger larval stages was enormously 

 large, proportionally, is a small group of follicles lined with col- 

 umnar or cuboidal epithelium (fig. 106). It is surrounded by con- 

 nective tissue and lies between the tongue muscle above and the 

 median venti'al cartilaginous bar below, with a large blood vessel 

 on either side. It extends, as Miiller says, from the second to the 

 fourth gill-pouch. The follicles are generally filled with a secretion 

 (not shown in the figures), and, with their surrounding cells, form, 

 in cross section, an oval mass. Usually from four to six follicles 

 are cut in each transverse section. 



Born was the first to describe correctly the salivary or basilar 

 gland in the lamprey, Rathke having mistaken the basilar muscle, 

 in which the gland lies imbedded, for the tissue of the gland, con- 

 sidering the true gland as merely the cavity. 



' Jenaische Zeitachrift, Bd. VII. 



