CONTENTS 

 I. Introduction 5 



II. The embryonic ground-plan of the lymphatic system in the trout 



upon which that of the adult is built 6 



III. Are the lymphatics of fishes transformed veins? 11 



IV. The modifications which the embryonic ground-plan of the lymphatic 



system undergoes in establishing the more advanced stages in the 

 trout 14 



V. The embryonic ground-plan of the lymphatic system in ganoids and 



the subsequent transformations which it undergoes 17 



VI. The development of the subocular lymph sacs in the trout 20 



VII. The development of the lateral pharyngeal lymphatic in the trout.. . 32 



1. The development of that portion of the lateral pharyngeal lym- 



phatic which lies anterior to the points at which primary com- 

 munications are established between it and the precardinal 

 (jugular) veins 33 



2. The development of that portion of the lateral pharyngeal lym- 



phatic which lies opposite to the points at which primary 

 communications are established between it and the precardinal 

 (jugular) vein 37 



VIII. The development of the superficial facial lymphatic in the trout 42 



IX. The development of the precardinal (jugular) lymphatics in the 



trout 44 



X. The development of the medial pharyngeal lymphatic 47 



XI. Variations in the rate at which the lymphatic system of the trout 

 develops in different embryos of the same age, as well as upon 

 opposite sides oi the same embryo 50 



XII. Do the peripheral lymphatics form a closed system of endothelial- 



lined vessels similar to those of the haemal system? 55 



XIII. General considerations concerning the genesis and growth of the lym- 

 phatic system in its relations to the haemal system 57 



Literature cited 72 



Plates 76 



3 



