PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 607 



are developed in the pharyngeal region of Amblystoma, the list 

 including the thyreoid, and thymus glands; the so-called post- 

 branchial body; the so-called epithelial bodies or gill-remnants; 

 and also the carotid gland, although it is not a true pharyngeal 

 derivative. 



Since but little recent work has been done on the develop- 

 mental side of these structures in amphibians — Maurer ('88), 

 Livini ('02), Greil ('02-06) and Marcus ('08) excepted— a detailed 

 study of their morphogenesis in Amblystoma has some value. 



The work has been carried on in the zoological laboratory of the 

 University of Illinois, under the direction of Professor Kingsley, 

 to whom the writer is deeply indebted for invaluable aid during 

 its prosecution. My thanks are also due Professor Ward, for 

 laboratory facilities and numerous other courtesies. 



Materials and methods 



This research is chiefly based upon the study of serial sections 

 of larvae of Amblystoma punctatum, beginning with 5 mm. stage, 

 and including successive stages through the 45 mm. larvae, and 

 following these with stages in transformation, and sections of 

 adult heads. Supplementing the study of the slides, gross dis- 

 sections were made of adults, using Amblystoma tigrinum as a 

 basis. The young larvae were fixed in Smith's fluid, stained in 

 toto in borax-carmine, dehydrated, imbedded and mounted in 

 the usual way; older larvae and adult heads were fixed in formalin 

 (heads decalcified), dehydrated, imbedded, sectioned and doubly 

 stained on the slide with borax-carmine and Lyons blue. 



For stages in metamorphosis, I am greatly indebted to Pro- 

 fessor Kingsbury of Cornell University, for the use of his excel- 

 lent slides, and my thanks to him for his kindness are here given. 

 The figures representing the various structures are drawn by the 

 aid of the camera lucida. 



