470 



ON THE ORIGIN AND EARLY DEVELOPMENT 



We first attempted to prevent the down-growth of lymphatics by inserting the tip 

 of a porcupine quill into the angle formed by the duct of Cuvier and posterior 

 cardinal veins in an embryo of 3 days, a stage at which this region is situated ante- 

 rior to the shoulder. However, when such embryos were examined two or three 

 days later it was found that this wedge had in no way interfered with the normal 

 development, for the veins were present in their normal position beneath the shoul- 

 der, while the plug had remained in the neck region anterior to the shoulder. As 

 might be expected, normal lymphatics were present over the side and connected with 

 the deeper plexus in a normal manner. 



Our next operation consisted in making a gap which would isolate the side 

 region from the region associated with the veins beneath the shoulder. This was 

 effected by removing the wing-bud and destroying a number of adjacent segments. 



FIG. 5. Normal chick of 5 1 clays, with superficial lymphatics injected with India ink. Compare with figure 6. X 12. 



Fio. 6. Chick from operation 2, with superficial lymphatics injected. Embryo was operated on at 2 days 23 hours. Somites 



17 to 20 were dissected away and the wing-bud removed. Three days later (when the chick was 5 days and 



18 hours old) the egg was reopened and the lymphatics injected. Comparison with figure 10, which shows the 

 superficial lymphatics of a normal embryo of the same stage of development, shows clearly that the side region 

 of the operated chick has been effectually isolated from the deep anterior point of origin. In spite of this fact 

 the lymphatics of the side region have developed normally. X 12. 



Fia. 7. Chick of 2 days IS hours which died soon after operation (operation 3). Six somites (22 to 27} were dissected away 

 together with the body-wall opposite them. The tail-bud posterior to somite 32 was cut off. X 12. 



The wing-bud was snipped off with iridectomy scissors and the segments dissected 

 away with fine needles and forceps. In the first operations of this series, in which 

 only three of the somites were injured, the gap produced was not large enough, and 

 the normal lymphatics of the side plexus, in chicks of 6 to 7 days, were found to 

 connect along the dorsal side of the hole with the deep cervical lymphatics connect- 

 ing with the veins. When four to seven segments, in addition to the wing-bud, 

 were removed, the result was a large "chasm." In these embryos, allowed to 

 develop two to three days after the operation, the jugular lymphatic plexus con- 

 nected with the veins was present, but no vessels running posteriorly from it through 



