I. INTRODUCTION 



My studies on the development of the lymphatic system in 

 fishes have thus far been confined to the vessels of the head and 

 pharynx. These vessels were chosen for the reason that they 

 have not been dealt with by others to any extent and because 

 they present a greater variety of conditions for study than those 

 situated in the trunk and tail regions. The fishes thus far 

 studied consist of ganoids and teleosts and include Amia calva, 

 Lepidosteus osseous, Salvelinus f ontinalis, Mitchill (brook trout), 

 Salmo Gairdneri, Richardson (steelhead trout) and Salmo irid- 

 eus, Gibbons (rainbow trout). The vascular system of be- 

 tween six and seven hundred trout embryos has been injected 2 

 and the embryos studied during the process of injection, in 

 transparent mounts after the method of Spalteholz, and in sec- 

 tions. Forty-two reconstructions have been made, after the 

 method of Born, of the arteries, veins and lymphatics in the 

 regions of the head and pharynx of Amia, Lepidosteus and the 

 trout. These reconstructions form a fairly complete series which 

 illustrate the development of the lymphatics from the time of 

 their earliest appearance in the embryo, as a series of discontinuous 

 anlagen or lymph vesicles, to the establishment of a condition in 

 which a continuous system of lymph channels is present. Since 

 the injection method has been employed in following the de- 

 velopment of the lymphatics in the trout, I will deal, for the 

 most part, with the conditions observed in this form. 3 



2 The embryos were injected by my Assistant, Mr. Charles F. Silvester, to 

 whom I am much indebted for his efficient services in this connection. 



3 I wish to express my thanks and appreciation to Professor Raymond C.Osburn 

 of -the New York Aquarium and to Commissioner Hugh M. Smith of the U. S. 

 Bureau of Fisheries, for their courtesy in supplying me with trout embryos. 



