376 ARTHUR WILLIAM MEYER 



preserved in toto jiiid then as much of the foetus as necessary 

 removed after fixation and used for the same purpose. 



It was possible to recognize macroscopically with some cer- 

 tainty, hemal nodes in the himbar region of sheep foetuses 12 

 cm. (V. B.) long and microscopically somewhat earlier (Meyer 

 '08). But as already stated, positive identification of the gross 

 or sectioned specimen was, to be sure, not always possible, 

 even in older foetuses. In serial microscopic sections it was 

 possible, however, to distinguish masses of lymphoid tissue 

 distinctly hemal in character in foetuses 9.8 cm. (V. B.). In 

 all of these young foetuses there is considerable difficulty, how- 

 ever, in distinguishing early developing lymphatic nodes from 

 hemal nodes because differentiating areas of mesenchyme which 

 might be regarded as early stages in the formation of lymph 

 nodes are frequently seen to be contiguous with others which 

 plainly suggest early hemal nodes. This difficulty is further 

 complicated by the fact that the lymphatics of developing lymph 

 nodes are often filled with blood or erythrocytes or at least 

 contain some blood. A further difficulty lies in the fact that 

 some developing hemal nodes of other species contained no 

 blood whatever thus suggesting a possibility of the occurrence 

 of a non-vascular type or form of anlage independent of the 

 lymphatic system in its early stages as held by von Schumacher, 

 '12, Forgeot, '09, and Piltz, '01. From these things it is evident 

 that confusion may easily occur where both types of nodes are 

 found in the same region. For evidently a non- vascular anlage of 

 a hemal node might incorrectly be assumed to be that of a lymph 

 node and a vascular anlage of a lymph node that of a hemal 

 node. However, the latter error, i.e., the designation of a very 

 vascular portion of such a differentiating area of mesenchyme 

 as hemal, instead of lymphatic, is not so likely to occur, because 

 the early even if not the earliest stages in the development of 

 lymph nodes although frequently vascular, show less inter- 

 mingling of blood and mesenchyine even when the lymph sin- 

 uses are filled with blood and their development is generally 

 considered to be preceded or at least accompanied by the for- 

 mation of a plexus of lymph channels. The latter, however, 



