The Origin and Development of the Lymphatic System. 55 



The jugular lymph plexus develops into a small sae (M tiler's fig. 6 I 

 which becomes a single jugular gland. This small, fusiform gland 

 has been studied by a number of observers and has been worked out 

 in all its relations by Jolly (59) in his interesting paper on the lymph 

 glands in buds. 



Miller (97, page t89) quotes Mierzewski as having seen rhythmical 

 contractions of the jugular lymph sacs. A reference to Mierzewski's 

 paper, however, will show that he consistently .-peaks of posterior 

 lymph heart and jugular lymph plexus and his reference to pulsation 

 (page 479) is a confirmation of Sala's observations in the posterior 

 lymph hearts. Miller notes the absence of muscle ami the point should 

 be emphasized, because the jugular lymph sac in birds becomes not 

 a lymph heart, hut a lymph gland. 



The iliac lymphatics in birds are very well brought out by .lolly 

 (59) in his article on lymph glands. He does not consider their 

 origin, but his fig. 15 shows their distribution extremely well, and his 

 fig. 11, pi. XI, gives the exact histological picture of a lymph sac with 

 connective tissue bridges for a bird on the 18th day of incubation. 

 This is the method by which the primary sacs become lymph glands, 

 as is shown in section VI. 



6. Primary Lymphatic System ix Amphibia, Anterior and 

 Posterior Lymph Hearts. 



It is not possible at this time to give a complete account of the 

 development of the lymphatic system of the amphibia and feptilia, 

 but enough evidence is at hand to show that the lymphatics are derived 

 from the veins. The remarkable subcutaneous lymph sacs in the frog 

 have always attracted interest and stimulated a curiosity to unravel 

 their development as was brought out by Langer (75) in 1868. Some 

 recent experiments of Abel (1) which combine anatomical and pharma- 

 cological methods add to this interest. 



Meltzer (95) had published experiments to show that a smaller dose 

 of a drug produced convulsions when injected into a cardiectomized 

 frog than into a normal one. He concluded that the drug traveled 

 through the tissue spaces. 



Abel found that a dye, acid fuchsin, when injected into the lymph 

 sacs of a normal frog was distributed widely over the body by the 

 blood vessels. In a cardiectomized frog a small dose injected into the 



