EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 273 



However, the term myeloid tissue, or myeloid metaplasis, is 

 used throughout the paper as a collective name, under which 

 all the characteristic cell elements of the bone-marrow are under- 

 stood, it is the erythroblastic, granuloblastic tissues, and re- 

 spectively the megakaryocytes. The terms promyelocytes, 

 metamyelocytes, mikromyelocytes, which correspond to inter- 

 mediate stages between a lymphoid hemocytoblast and a leuko- 

 cyte are omitted. These stages are characterized by unessential 

 features and are often overstepped in embryonic life during 

 intensive regeneration. The use of so many terms for expressing 

 small differences between development stages in a cell lineage 

 seems more to confuse than to help. For this reason I did not 

 introduce them lately in the scheme given in the Anatomical 

 Record, and in the present paper, only terms which designate 

 definite morphologically well defined stages will be used, and 

 these are lymphoid hemocytoblast, granulocytoblast, and granu- 

 locyte or leucocyte. 



The reciprocal relations in the lymphatic cell group are some- 

 what more obscure. The different lymphatic cells are looked 

 upon by Maximow (25) and Weidenreich (44) as being merely 

 temporary appearances of young undifferentiated cells, all 

 characterized by the same differentiation potentialities. Though 

 these authors admit a specific morphological structure for the 

 large and the small lymphocytes and the histogene wander cell, 

 yet they assume that these cells may easily change reciprocally 

 their structure according to the environmental conditions. In 

 birds and reptiles (Danchakoff (9)) as well as in mammals 

 (Maximow (25)) it is easily demonstrated that small lympho- 

 cytes may both proliferate and differentiate further, but their 

 lines and products of differentiation are not identical with those 

 of the large lymphocytes (Pappenheim (32), Danchakoff (9) ). 

 Neither is it proved definitely that the small lymphocytes may 

 grow into the large. Nor is a possibility of erythrocyte develop- 

 ment at the expense of small lymphocytes shown to exist in 

 birds and reptiles, as Freidsohn (14) admits lately for amphib- 

 ians and Venzlaff (43) for birds. Therefore, under the name 

 of small lymphocyte, cells characterized both by a definite 



