288 GEO. S. HUNTINGTON 



West has studied the development of the caudal lymph heart 

 in embryos of the chick with fully injected blood vessels. His 

 results will shortly be published in full. I am permitted to quote 

 the following conclusions from the summary of his paper: 



1. The mesenchyme lateral to the caudal muscle plate, and caudal 

 to the hind limb bud, presents in 10.5 mm. embryos, between the points 

 of penetration of the first five coccygeal veins, an enlargement of the 

 interstitial spaces, which soon fuse with one another, by the breaking 

 down of the mesenchymal processes, to form disconnected uninjectible 

 lacunae, bounded by mesenchymal cells which become flattened to form 

 an endothelium. 



2. The lacunae adjacent to the lateral branches of the first five 

 coccygeal veins establish secondary connections with these veins just 

 lateral to the point at which the veins penetrate the caudal muscle 

 plate, while more distally developed mesenchymal spaces successively 

 add themselves to those already connected with the vein?. 



3. Simultaneously with the formation of the mesenchymal lacunae 

 the adjacent mesenchyme exhibits areas of active haemopoesis, in which 

 mesenchymal cells in all transitional stages of differentiation into ery- 

 throcytes and lymphocytes are found. In addition, some erythrocytes 

 develop directly from the endothelial cells lining the mesenchymal 

 spaces. 



4. The red blood cells thus formed become included within the lumen 

 of the lymphatic lacunae in one of two ways: 



(a) Some blood cells find their way into the lymphatic lacunae by a 

 constant breakmg down of the mesenchymal processes during the en- 

 largement of the lymphatic spaces. 



(b) Other blood cells gain direct access to the interior of the lym- 

 phatic channels by migration through the latter's endothelial walls. 



These intralymphatic red blood cells are conveyed into the haemal 

 circulation through the lateral branches of the first five coccygeal veins. 



Thus the lymphatic plexus, which subsequently forms the posterior 

 lymph heart, has assumed at this stage of its development not only a 

 haenwpoetic, but also a haemophoric function. 



We have here a group of four independent observers investi- 

 gating the development of the caudal lymph hearts in a wide 

 range of vertebrate embryos, avian, chelonian, anure amphibian 

 and cyclostome. The results of all four investigators show a 

 remarkable unity of conclusions. They do not all touch on 

 every phase of the problem, but their combined findings yield, 

 for the interpretation of the ontogeny of the caudal lymph hearts 

 of vertebrates, of their connections with the systemic lymphatic 



