490 



follows. By Wilms and others certain tumours, not by any means 

 all, are referred to cleavage- cells, not identified as germ-cells, but 

 really destined to form some part of the embryonic body. These 

 cleavage-cells are supposed to be "shunted" from the normal connection 

 at some very early, but not defined, period of the development. As 

 so derived, they are parts of the organism, in which they occur. The 

 writer's conceptions, on the other hand, may be stated in the following. 

 A tumour is a more or less reduced, more or less incompletely 

 differentiated, sterile Metazoan (animal) organism. It starts by the 

 abnormal development of an aberrant or vagrant primary germ-cell, 

 and, growing under conditions unfavourable for the complete and 

 normal differentiation of all its parts, it unfolds and develops those 

 things, for whose growth the nidus is suitable, the rest degenerating, 

 or remaining latent. In this way it is seen, that the physiological 

 nidus accounts for the frequent "mimicry" by tumours of their sur- 

 roundings. As derived from primary germ-cells, tumours are never 

 parts of the organism, in which they occur (contra Wilms), but they 

 are its reduced sisters or brothers, identical with it in ultimate 

 characters. They never arise from cells, which at any time may be 

 regarded as cells of the individual. Exactly as identical twins are 

 the products of two sister or brother germ-cells, identical in ancestry 

 from the same primitive germ-cell, and alike in all ultimate characters, 

 so also any animal and a tumour within it, say, a sarcoma or tumour 

 of embryonic tissue, stand in the same relations of ancestry from one 

 primitive germ-cell; and have the same ultimate characters at the 

 starting point of their development. But, unlike fully developed 

 identical twins, the individual and its tumour develop in different 

 directions; the one upwards along the track of higher and higher 

 organisation, the other downwards along the roadway of abnormality, 

 of degeneration, of arrest, at times even of riot, destruction, and 

 disaster. 



Postscript. The foregoing abstract forms a continuation and 

 extension of the chapter on "Dermoid Cysts and Teratomata" in a 

 memoir 1 ), recently published by me. On p. 671 it was written: "how, 

 it may be asked, shall one limit the possible reduction of an embryoma? 

 Where shall the line be drawn?" The present writing offers the 

 answer to that question. As the writer suspected in 1900, no line 



1) J. Beard, The Germ-cells, Part 1, Raja batis. Zool. Jahrb., 

 Anat. Abteil., Bd. 16, 1902, p. 615—702, loc. cit. p. 669. 



