304 GEO. S. HUNTINGTON 



In the reptilian embryo the greater number of the important 

 systemic lymphatic sinuses, produced by the fusion of these 

 earlier anlages, develop without any relation whatsoever to the 

 embryonal veins, as independent periarterial channels. Conse- 

 quently in the reptilian embryo the question of their direct or 

 indirect origin from the veins never even arises. Only a small 

 number of the reptilian systemic lympatics follows the embryonal 

 veins, surround them and in some instances replace early venous 

 lines. 



The early anlages of the reptilian jugular lymphsacs are in 

 my opinion without doubt primitive haernophoric lymphatics in 

 the sense above defined for the homologous anlages of the mam- 

 malian jugular sacs {vida supra, pp. 273-280). 



This is especially true for the element which I described in 

 the publication previously quoted (12) as the posterior or cau- 

 dal division of the ventral veno-lymphatic sinus in lacertilian 

 embryos. 



For the purpose of comparing the development of the sys- 

 temic lymphatic system in embryos of the three amniote classes 

 it is perhaps best to contrast the typical ontogenetic stages in 

 a single and definite area in each. The region of the main axial 

 systemic lymphatic channels (thoracic ducts) are thus contrasted 

 in the series of diagrams shown in figures 18 to 20. 



1. In the reptile (chelonian and lacertilian embryos-) the large 

 adult periaortal lymphatic sinuses develop at first as small inter- 

 cellular clefts in the spongy mesenchyme surrounding the dorsal 

 aortic arches and their caudal prolongation as the single trunk 

 of the dorsal aorta (fig. 18, A, 2). These spaces enlarge, approach 

 each other, fuse and finally surround the aorta as a huge peri- 

 arterial lymphatic sinus, with trabeculae in the interior, repre- 

 senting remnants of the original partitions between the com- 

 ponents of the sac (fig. 18, B, 3). This extensive periaortal sinus 

 represents in Lacertilia and Chelonia the much reduced thoracic 

 ducts of birds and mammals. It establishes secondary connec- 



2 Aspidonectes spinifer; Chelydra serpentina; Chrysemys marginata; Chry- 

 semys picta; Pseudemys scripta; Cnemidophorus sexlineatus; Sceloporus un- 

 dulatus. 



