476 



ON THE ORIGIN AND EARLY DEVELOPMENT 



without tails, with a large gap in the body-wall on the right side anterior to the leg, 

 and with the right leg smaller than usual and possessing two toes. On the left side 

 a continuous plexus of superficial lymphatics was injected over the side, pelvis, and 

 stump. On the right side the plexus anterior to the gap in the axillary region was 

 normal in appearance, and over the posterior part of the pelvis and stump a normal 

 lymphatic plexus was injected with ease. In other words, the result was identical 

 with that obtained in experiment 3. The operation was repeated in the same 

 manner except that in this case only two somites were left untouched in the region 

 opposite the anterior portion of the right leg, and the leg was bisected, the posterior 

 half and the three remaining segments opposite it being removed. 



In this operation 6 embryos were opened at varying incubation ages. Plate 

 7 and text-figures 14 and 15 illustrate their appearance at 7 and 7| days respectively. 



FIG. 14. Left side of a chick of 7 days 

 and 12 hours. Normal except for ab- 

 sence of tail. Superficial lymphatics 

 injected. Compare with right (op- 

 erated) side shown in figure 15. X 5. 



FIG. 15. Right side of the same em- 

 bryo shown in figure 14. Example of 

 operation 4. At 2 days 18 hours incu- 

 bation the three segments anterior to 

 the posterior limb-bud of the right 

 side were dissected away, together 

 with the body-wall opposite them; 

 and, in addition, the two segments 

 opposite the anterior part of the leg; 

 the next two segments, with the limb- 

 bud opposite, were left intact, and 

 the next three, opposite the posterior 

 part of the leg, were dissected away, 

 the liml>-bud bisected and the pos- 

 terior half removed. The operation 

 was completed by removing the tail. 

 Compare appearance of embryo 

 with chick shown in plate 7, a 

 younger specimen from the same 

 type of operation. The injected 

 lymphatics of the shoulder region 

 and axilla were present and normal 

 in appearance. Over the pelvis and 

 tail stump in this and other embryos 

 from operation 4 no lymphatics 

 could be injected. X 5. 



The gap anterior to the leg and the rounded stump characteristic of operation 3 are 

 noticeable, and in addition the right leg may be seen to be deformed and to possess 

 only one toe. 



Four of the embryos were opened at 65 to 7J days (the stage illustrated in 

 plate 7, figure 33) and the lymphatics injected. The left side was tested first and 

 the injection showed the presence of the continuous plexus described in operations 

 1 and 3 (left side). On the right side normal lymphatics were injected in the supra- 

 scapular region, in the region beneath the shoulder, in the axilla, and as far pos- 

 terior as the gap in the body-wall. However, when the region over the pelvis was 

 tested, repeated careful injection failed to show any sign of a lymphatic plexus. The 

 injected ink, instead of remaining in blebs, as is usual in the case of extravasations 

 in the subcutaneous tissues, spread out rapidly through the tissue in finger-like 

 projections which finally ran together and made a continuous black sheet. That 



15 



