Anatomy and Development of Posterior Lymph Hearts of Turtles. s.'> 



FIG. 3. Transverse section through lymph heart 

 region of Loggerhead Turtle embryo No. 232. 

 (22 days, 15 mm.) Xioo. a, veno-lymphatic 

 channels; b, vein. 



A careful study of such a series of sections can not fail to convince 

 the observer that these spaces play a far greater part in the development 

 of the lymphatics and even of 

 the lymph hearts than is now 

 usually supposed. By the six- 

 teenth day another change takes 

 place which greatly accelerates 

 the development of the lymph 

 hearts. This is brought about by 

 the longitudinal anastomosis of 

 the segmental branches of the 

 postcardinal veins caudad of the 

 opening of the iliac veins and 

 outside of the muscle plates. The 

 veins thus formed continue cra- 

 nially as the most important 

 branches of the posterior renal 

 advehent veins, and caudally as 

 the lateral coccygeal veins of the 

 tail. The formation of these 

 veins together with the tapping 

 of the mesenchymal spaces allows 

 a much more complete and rapid 

 drainage of the lymph from pos- 

 terior limbs and tail than was hitherto possible. The capillaries of the 

 region subsequently to be occupied by the lymph hearts increase 



enormously in size and fuse 

 with each other to form several 

 large, anastomosing spaces, the 

 veno - lymphatic channels. 

 These channels extend parallel 

 with the pair of newly-formed 

 veins mentioned above, and 

 communicate with them at two 

 or three points. 



In an embryo 20 days old 

 (fig. 2) the segmental connec- 

 tions between the postcardinals 

 and the recently formed com- 

 mon coccygeal veins are still 

 retained. The anlagen of the 

 lymph hearts are scarcely dis- 

 tinguishable from the veins in 

 this stage. At 21 days of de- 

 velopment, the mesenchyme 

 cells begin to condense around 

 these veno-lymphatic channels 

 to form definite walls of con- 

 siderable thickness and density. Muscle cells also wander in from the 

 adjacent muscle plates and become involved in the formation of these 



FIG. 4. Transverse section through left lymph heart of 

 Loggerhead Turtle embryo No. 236. (25 days, 17 

 mm.) v, vein; l.h., lymph heart; n.g., nerve ganglion. 



