84 Papers from the Marine Biological Laboratory at Tortugas. 



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Fig. s. — Transverse section through left lymph heart of Log- 

 gerhead Turtle embryo No. 228. (32 days, 40 mm.) 

 V, vein; l.li., lymph heart. 



walls. These channels continue to increase in size and complexity 

 through the twenty-second and twenty-third days. Figure 3 represents 

 a section taken through the region of the posterior lymph hearts of an 



embryo 22 days old. The 

 lower lymph space opens 

 into the vein by a valve- 

 like opening. From the 

 24-day stage on, the par- 

 titions between the several 

 veno - lymphatic channels 

 begin to break away in the 

 anterior part of the heart 

 region, forming fewer and 

 larger spaces. Figure 4, 

 from an embryo of 25 

 days, shows a section taken 

 through the middle portion 

 of the lymph heart. 



The formation of the 

 lymph hearts is well ad- 

 vanced in embryos of 32 

 days and older. Figure 5 

 shows the relation of the 

 lymph heart to the vein 

 and lymph spaces in a 3 2 -day embryo. The process of the atrophy 

 of the walls separating the several lymph heart anlagen continues 

 from before backward until at the time of hatching there seems to be 

 a single cavity present for each heart. In this, as well as in several 

 other points, the development of the lymph hearts of the sea turtles 

 differs from that of fresh-water turtles. In the mud turtles the spongy 

 character of the hearts is retained, to some extent, in the adult animal. 



GENERAL CONCLUSIONS. 



Recent investigations of the ontogeny of the lymphatic system of 

 mammals have given rise to three general theories. Two of these agree 

 in deriving the lymphatic system entirely from the venous system, 

 while the third assigns to it, in part at least, an independent origin. For 

 purposes of comparison with the results obtained by the writer from a 

 study of the development of the posterior lymph hearts of the logger- 

 head turtle, a very brief resume of these several theories will be given at 

 this point. 



(i) The theory of the confluence of independent spaces to form con- 

 tinuous channels. — This view, which is the one formerly held by most 

 embryologists, is now held in a modified form by Huntington (1908-10). 

 According to this writer: 



The peripheral general lymphatic channels appear to be developed by the 

 confluence of spaces independent of the venous system, although closely associated 

 with the same. * * * They begin as minute extra-venous vacuoles, closely 

 applied to the surface of the veins which they accompany. They enlarge as the 

 lumen of the vein diminishes. They become confluent with each other, but never 

 contain red blood-cells, nor do they commvmicate with the blood channels. 



