1902,] NATURAL SCIENCES OF PHILADELPHIA. 85 



STRUCTURE AND DEVELOPMENT OF THE THYROID GLAND IN 

 PETROMYZON. 



by albert m. reese. 

 Introduction. 



The material with which the following work was doue was of two, 

 or possibly three, species. The first species was Petromyzon jjlaneri, 

 the small lamprey that, in the adult condition, reaches a length of 

 about six inches only. This first lot of material was collected by 

 Dr. R. G. Harrison at Naples. It included stages from the re- 

 cently fertilized egg to the swimming larva, in which the yolk was 

 no longer externally visible and in which the mouth was separated 

 from the pharynx only by a thin partition of cells. This oldest 

 stage was killed fourteen days after fertilization. 



The second lot of material was obtained at Ithaca, N. Y. , and 

 probably mcludes larvse of both P. dorsatus, Wilder (lake lamprey) 

 and P. branchialis (brook lamprey), as both species are known to 

 spawn in the same nest, and it is impossible to tell to which species 

 the larvse belong. Part of this lot of material was sent me 

 through the courtesy of Prof. S. H. Gage, of Cornell ; the rest I 

 myself obtained from one of the ' ' nests " in a stream at Ithaca, 

 New York. 



I wish to express here my gratitude to my friend. Dr. Ross G. 

 Harrison, for placing at my disposal the material from which the 

 younger stages of development were made out; to Prof. Simon H. 

 Gage for the really considerable amount of trouble he took in aiding 

 one Avho was, at the time, wholly unknown to him, to obtain the 

 older stages for this work ; and to Prof. Brooks for much valuable 

 aid and many suggestions during the progress of the work. 



I obtained the best results by killing in corrosive acetic (95 cc. 

 saturated solution of HgCl^ and 5 cc. glacial acetic acid), harden- 

 ing in the usual alcohols and staining in toto with borax carmine, 

 and on the slide with Lyon's Blue. The greatest technical diffi- 

 culty experienced was in obtaining good i)reparations of the long 



