. Carnegie Institution of Washington publication. 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 h
. Carnegie Institution of Washington publication. 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
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