ATJTHOR'S abstract of TH18 PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, MARCH 30 



THE BRANCHIAL DERIVATIVES OF THE PIED-BILLED 



GREBE, WITH SPECIAL CONSIDERATION OF THE 



ORIGIN OF THE POSTBRANCHIAL BODY 



CHARLES EUGENE JOHNSON 



From the Department of Animal Biology of the University of Minnesota 



THIRTEEN FIGURES 



INTRODUCTION 



The development of the thymus and associated derivatives of 

 the gill pouches has been fully investigated in but a very few 

 species of birds. Recently our knowledge has been extended by 

 Helgesson's ('13) work on the common house sparrow, Passer 

 domesticus, and by the study of Hamilton, of the same labora- 

 tory, on the development of the thymus in the duck. Preceding 

 these among the more recent literature there is to be mentioned 

 the work of Kallius ('05, '06), in which the gill pouches are 

 treated in connection with the development of the tongue in the 

 duck and in the house sparrow, and that of Rabl ('07) on the 

 origin of the postbranchial body in the duck. 



Some years ago a study of the development of the thymus^ in 

 the pied-billed grebe, Podilymbus podiceps (Linn.) was under- 

 taken by me, with rather inadequate material. Recently, with 

 additional and also more advanced stages, this study has been 

 repeated, and since the grebe represents a low order of present- 

 day birds and one not previously investigated in this connection, 

 the later results, which in some respects differ from those of the 

 first attempt, are here submitted as a slight addition to the 

 subject of the gill pouches and their derivatives in birds. 



* The development of the thymus in the pied-billed grebe. Subject of a 

 thesis forming part of the requirements for the master's degree, under the super- 

 vision of Prof. H. F. Nachtrieb. Abstract appeared in Science, vol. 27, 1908. 



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