GASTRULATION IN THE PIGEON'S EGG— A MORPHO- 

 LOGICAL AND EXPERIMENTAL STUDY/ 



J. TIIOS. PATTERSON. 

 TABLE OF CONTENTS. 



PAGE 



I. lutrodiiction — Statement of Problem 65 



II. Material and Methods G7 



III. Gastrulation 73 



A. Study of the Developing Egg 73 



B. Study of Sections 78 



a. Pregastrular Stages 78 



b. Gastrulation Stages 80 



( 1 ) Invagination 8G 



Experiment I 88 



(2) Middle and Late Gastrulation Stages 92 



Experiment II 93 



Closing of the Blastopore 100 



Interruption of the Posterior Zone of Junction 103 



c. Postgastrular Stages 103 



IV. Experimental Studies 108 



Set A. On Early Gastrular Stages 109 



Experiments III-V 110 



Set B. On Late Gastrular Stages 112 



Experiments VI-VIII 112 



Set C. On Unincubated and Early Incubated Stages 113 



Experiments IX-XIII 114-116 



V. Discussion and Summary 116 



Discussion 116 



Summary ll<j 



Literature Cited 121 



C'ommon Reference lietters Used in the Figures 123 



Plates, I-X. 



I. Introduction. 



In view of the- fact that the bird has long been the classic type 



in the field of embryological research, it is surprising that the 

 question of the origin of the entoderm^ in this form should have 



'From the Department of Zoology, University of Chicago. 



^The terms entoderm, gut-entoderm, and invaginated-entoderm will be used 

 synonymously throughout this paper. 



TiTE .TouRNAL OF MoRrnoLOOY — Vol. XX, No. 1. 



