384 ARTHUR WILLIAM MEYER 



sible to demonstrate the pre-natal or even early post natal pres- 

 ence of a number of anlagen comparable to the number of hemal 

 nodes often found in the lumbar sub-vertebral region of sheep. 

 However, this difficulty could apparently be met by v. Schu- 

 macher's suggestion that lymph nodes — among which he in- 

 cludes hemolymph nodes — probably continue to form in post 

 natal life. As stated by others and also by myself (Meyer 

 '14) this is a conclusion which it is difficult to escape in the case 

 of both hemal nodes and of some supernumerary spleens. 



Then there are, of course, the fundamental structural differ- 

 ences between hemal and lymph nodes which must be met by 

 those who assume a conversion of one type of node into the 

 other and also a reconversion into the original form or type. 

 I previously called attention and emphasized the difficulty 

 involved in other papers of this series. Most if not all of those 

 who assume such easy conversions and reconversions between 

 lymph and hemal nodes have largely overlooked or must have 

 disregarded, the fact revealed especially by injections, that hemal 

 and lymph nodes are distinct and separate types. This is 

 true not only as far as the absence of lymphatics and all struc- 

 tural differences implied thereby are concerned, but also be- 

 cause of the entirely different character of the vascular circu- 

 lation within the node itself. Furthermore there are other less 

 crucial but nevertheless equally essential structui^l differences 

 between the two, besides the developmental considerations 

 here reported. 



Although Retterer made no special study of hemal nodes 

 his long series of morphological aaid experimental investiga- 

 tions on lymph nodes entitle his opinion to much consideration. 

 Since Retterer considers lymph and hemal nodes identical a 

 short statement of his idea of the development and to some 

 extent of the function of lymph nodes seems pertinent. Ret- 

 terer '06 found that the earliest lymph nodes in the inguinal 

 region of the sheep appear as continuous cell masses certain 

 elements of which become free from the protoplasmic 'font' 

 and transform themselves at first into lymphocytes and then 

 into erythrocytes. Their development begins as a syncytium 



