AUTIIOU S ABSTRACT OF THIS PAPER ISSUED BY 

 THE BIBLIOGRAPHIC SERVICE, DECEMBER 15 



VESTIGIAL GILL-FILAMENTS IN CHICK EMBRYOS 



WITH A NOTE ON SIMILAR STRUCTURES 



IN REPTILES 



EDWARD A. BOYDEN 



Harvard Medical School, Boston, Massachusetts 



THREE TEXT FIGURES AN"D FOUR PLATES 



Since Rathke's discoveries in 1825, biologists have been inter- 

 ested in the branchial region of amniotes as supplying the most 

 conspicuous example of the persistence of ancestral structures in 

 the higher vertebrates. But no record has yet appeared, with 

 the possible exception of Grosser's note on young human em- 

 bryos, which reveals the presence of any structures on the gill 

 arches of reptiles, birds or mammals, that can be interpreted as 

 functional or rudimentary gill filaments. Rathke, indeed, de- 

 scribed small, obliquely-placed plates (Blattchen) on the gill 

 arches of mammalian embryos but in 1832 he stated that their 

 irregular appearance made him very suspicious, and when he 

 examined them more carefuUy, in a sheep embryo which had 

 been in spirits some weeks, he became convinced that the leaf- 

 lets were merely broken-down fragments of delicate branchial 

 epithelium. 



WTiile studying the anatomy of the five-day chick and unaware 

 of Rathke's earlier attempt to find gills in mammals, my atten- 

 tion was attracted to ectodermal proliferations, protruding from 

 behind the hyoid arch, which seemed to be involved in the obliter- 

 ation of the cervical sinus. i To Professor F. T. Lewis I am in- 

 debted for the suggestion that these projecting cell clusters might 



' These were described briefly on page 18 of the following paper: "An anatomi- 

 cal study of the 13 mm. chick; a contribution to the comparative embryology of 

 birds and mammals." (Manuscript deposited in Harvard College Library, June 

 1916.) See also Proc. Am. Assoc. Anat., Anat. Rec, vol. 10, 1916, p. 185; vol. 11, 

 1917, p. .329. 



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