82 HENRY MCELDEERY KNOWER 



send the customary tributaries to the vertebral, and finally 

 large accessions are also received from veins of the body wall 

 which have spread over the surface from the great cutaneous 

 artery. This artery can be traced in the figure along the 

 mid-lateral wall of the abdomen from its origin in front of 

 the pronephros. It connects anteriorly with the facial system, 

 and ventrally its veins join those of the anterior abdominal 

 vein. The great cutaneous vein runs parallel and medial to 

 the artery, and connects anteriorly with the second inter- 

 segmental vein. As explained, this is the latest stage which 

 demonstrates clearly both early and late conditions of the 

 segmental veins. 



In older stages, the picture is much altered. The details 

 of the tributary plexuses of the vertebral and the segmental 

 series are then not distinctly seen because of overgrowth of 

 the superficial tissues and vessels, and the prominence of late 

 larger vessels is confusing. 



The anterior lymph heart is attached to the lower ventral 

 segment of the third vein, and is over-arched by veins from 

 the body wall, as in earlier stages. 



The lymphatics of this stage resemble closely in their main 

 features the system shown in figures 30 and 31; though they 

 are not so far developed, as indicated in the caudal plexus of 

 figure 33 for the lymphatics of the 12-mm. R. palustris before 

 the appearance of limb buds. 



Although much can be learned from double injections in 

 two colors, it is evident that study of separate pictures of the 

 lymphatics and blood vessels is demanded for these late 

 stages, on account of the overgrowth of lymphatics by the 

 superficial structures. 



