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ON THE OR GIN AND EARLY DEVELOPMENT 



On examining an embryo of this kind which had been allowed to develop until 

 it was 7 days old we found a gap in the body-wall anterior to the leg which extended 

 dorsally as far as the dense tissue around the spinal cord (where lymphatics are 

 never found at this stage), and which exposed the abdominal viscera. The amnion 

 was often attached along the borders of the gap. 



Injection of the left side of the embryo (the unoperated side except for the 

 removal of the tail) showed a continuous lymphatic plexus which extended from the 

 deep jugular plexus connected with veins, through the axilla, down the side, over 



FIG. 8. Left side of a chick of 6 days. This 

 side is normal except for the absence of the 

 tail. Continuous superficial lymphatic 

 plexus injected with India ink. This serves 

 as a control for the right side of the same 

 embryo shown in figure 9, which is an ex- 

 ample of operation 3. X 12. 



FIG. 9. Right side of same embryo shown in 

 figure 8. Chick of 6 days. Example of 

 operation 3. At 2 days and 12 hours the 

 six segments anterior to the posterior limb- 

 bud of this embryo were dissected away, 

 together with the body wall opposite. The 

 tail was then cut off. Lymphatics injected 

 with India ink. The vessels anterior to the 

 gap are normal in appearance and extent. 

 Over the posterior part of the pelvis a lym- 

 phatic plexus, normal in appearance but 

 less extensive than usual, was injected. 

 No lymphatics were injected on the an- 

 terior portion of the pelvis or over the 

 stump. Compare with the lymphatics of 

 the opposite side shown in figure 8. X 12. 



the pelvis and to the posterior stump, where the vessels were fine and delicate. 

 Lymphatics were also present in the region dorsal to the shoulder connecting, 

 anterior thereto, with the deep jugular plexus, but not yet posteriorly with the side 

 lymphatics. In other words, this left side possessed a lymphatic plexus of the type 

 described in operation 1, normal everywhere except for the absence posteriorly of 

 the beating lymph-heart and the consequent primitive character of the vessels over 

 the posterior tip of the pelvis (fig. 8) . 



On the right side our injections showed anteriorly the presence of normal 

 lymphatics in the deep jugular region, in the region dorsal to the shoulder, in the 

 axilla, and also in that portion of the side region anterior to the gap. Here, at the 

 edge of the gap, the lymphatic injection ended in a number of delicate points. 

 Repeated injections over the anterior part of the pelvis and leg in operated chicks 

 of this stage failed to show any lymphatics corresponding to those present in this 

 region in normal embryos or to the plexus already injected on the opposite side. 

 But by plunging the cannula into the tissue more posteriorly, over the proximal part 

 of the pelvis, a plexus of lymphatic capillaries of normal appearance, richness, and 

 location was injected with ease (fig. 9). 



