OF THE LYMPHATIC SYSTEM OF THE CHICK. 467 



the egg so as to bring the window on top, and waiting for a few moments until the 

 embryo moves around under the opening. The proper time at which to reopen the 

 egg can also be determined in this way. 



At the desired time, the mica was removed and the embryo again exposed. 

 The presence of lymphatics was then tested by injections with India ink. In many 

 of the experiments injection of the left side served as a control for the operated side. 

 In some specimens the blood-vessels were subsequently injected with Berlin blue 

 gelatin (5 per cent). The embryos were fixed in Carnoy's solution, dehydrated in 

 three changes of absolute alcohol and cleared in benzol and oil of wintergreen. In 

 cases where it was desired to section, the specimen was fixed in Bouin's fluid and 

 stained by the same method described in Part I. 



OPERATION 1. REMOVAL OF THE POSTERIOR LYMPH-HEART REGION. 



The first operation consisted in the removal of the posterior lymph-heart 

 region before the development of any posterior lymphatics. Since our other studies 

 had made us familiar with the normal appearance of the lymphatic plexus which 

 develops in this region, and since we had studied the invasion of the neighboring 

 region (the posterior tip of the pelvis) by lymphatics connected with this plexus, 

 this appeared to be the logical place for starting such an experiment. We therefore 

 removed the tail in chicks ranging in age from 2 days 14 hours to 3 days, a stage at 

 which 37 to 40 somites have differentiated. All of the tail region posterior to the 

 thirty-third or thirty-fourth segment was snipped off with iridectomy scissors. 

 The operation is comparatively simple, although a good deal of bleeding frequently 

 follows the cutting. The total mortality amounted to 50 per cent, when precau- 

 tions were developed for preventing the embryo from sticking to the shell. The eggs 

 were returned to the incubator and development allowed to continue. They were 

 reopened at intervals of 3 to 5 days after the operation, the lymphatics injected 

 on both sides of the embryo, and their character and extent compared with those of 

 normal chicks of a corresponding stage. Since healthy operated chicks were found, 

 in most cases, to be delayed about 12 hours in their development, the injected 

 embryos corresponded to chicks of 5 days 20 hours, up to 7 days 20 hours. These 

 chicks developed with well-rounded stumps instead of tails, and the posterior 

 lymph-hearts were absent. 



In a normal chick of 5 days 20 hours lymphatics can be injected in the region 

 of the thoraco-epigastric vein between the two limbs, where they form a plexus 

 which connects through the axillary region with the deep jugular plexus, which in 

 turn connects with the anterior and posterior cardinal veins in the region of the 

 duct of Cuvier. Posteriorly, the lymph-heart plexus, with its venous connections 

 and its superficial extensions over the posterior tip of the pelvis, can be injected 

 (fig. 5). In operated chicks of this stage (6 days) the side plexus was readily in ject- 

 ible and entirely normal in appearance ; but diligent search by means of many care- 

 ful injection tests failed to reveal any posterior lymphatic plexus over the pelvis 

 or stump. In embryos allowed to develop longer and examined when 6| to 7 days 

 old (or the stage corresponding to normal 6 to 6| day chicks), a few ink granules 



