OF THE LYMPHATIC SYSTEM OF THE CHICK. 477 



the failure to inject the lymphatics in the right side was not due wholly to the con- 

 dition of the tissue is evidenced by the fact that in many of these embryos the tissue 

 over the pelvis of the left side was more edematous than that of the right side, and 

 yet lymphatics were always injected on the left side at the first insertion of the 

 cannula. 



The results of the injection te^ts in operation 4 made it appear as if the answer 

 to this part of our problem had at last been found. One of these embryos (shown 

 in plate 7, fig. 33) was selected for sectioning. As may be seen, the gap in the body- 

 wall anterior to the leg was sufficiently large to isolate the leg and pelvis from its 

 anterior source of supply, while the rounded stump and deformed leg, with only 

 one digit, exactly resembled the condition present in the four other embryos just 

 described. In this specimen we refrained from testing for lymphatics the region 

 over the pelvis of the right side, since we feared that the extravasations thus pro- 

 duced might obscure the cytological picture. On the left side we injected a small 

 amount of Berlin blue, enough to demonstrate the presence of a normal lymphatic 

 plexus. The blood-vessels were then injected completely, the embryo was fixed 

 in Bouin's fluid, dehydrated, cleared, and sectioned according to the method 

 described for the studies in Part I. 



In studying the sections of the pelvic region we found a number of irregular 

 vessels which had not received the injection mass. In reconstruction it was found 

 that these vessels were located, for the most part, in the layer beneath the super- 

 ficial blood-capillaries, some of them coming to the surface in the interstices between 

 blood-vessels. From their location and general appearance there appeared to be 

 no doubt that these vessels were indeed lymphatics. They differed considerably 

 in character from normal lymphatics of this stage and were not so large or nearly 

 so numerous as the lymphatics of the opposite side. Although these vessels formed 

 a plexus in places, this resembled the more primitive type formed by the earliest 

 lymphatics described in Part I, except for the greater size of some of the component 

 vessels. Many of the connections were very narrow and others were thread-like 

 and solid. The absence of any extensive lymphatic plexus over the pelvis after 

 operation 4, and the lack of any continuous lumen in the scanty plexus which was 

 present, undoubtedly accounted for our failure to inject lymphatics in other chicks 

 of this series. It is significant that these are the same factors which prevented 

 injections of the earliest lymphatics described in Part I. 



This straggling lymphatic plexus, peculiarly primitive in many respects and 

 much less luxuriant than usual, was for the most part independent of the surround- 

 ing blood-vessels. However, certain of these irregular vessels possessed an 

 undoubted connection with an injected blood-vessel. They were in no wise dis- 

 tinguishable from the other vessels of the plexus and differed markedly from the 

 straight, regular, and narrow blood-vessel sprouts. Moreover, no such "sprouts" 

 were found on the left side of this embryo, where, as has been indicated, a normal 

 and extensive lymphatic plexus interlaced with the blood-capillaries without com- 

 municating with them. From the earlier studies, reported in this paper, of the 

 characteristics of the earliest lymphatics and their relation to blood-vessels, there 



