THE NATURAL HISTORY OF TUMOURS 559 



are in existence ; and in animals so highly specialised as 

 frogs, ova that have never been fertilised by spermatozoa 

 can be made to develop even into the tadpole stage by applying 

 a suitable chemical stimulus. The same thing within narrower 

 limits is true of the germ organ in man. It may not be possible 

 for it to give birth to a new and perfect individual, but in 

 embryonic life at any rate its power of direct reproduction is 

 strong enough to enable it to give off buds capable of growing 

 into highly complex structures ; and though as development 

 advances, the range and strength of this power diminish, what 

 is left of it can be called into action at almost any time if a 

 suitable stimulus is applied. 



Tumours that Grow from Germ Cells 



The growths that originate by direct reproduction from 

 the germ organ and its derivatives (especially the ovary) 

 assume many different forms. The most elaborate spring 

 from the as yet undifferentiated germ organ, in the earliest 

 moments of existence, before the ovary and testis are formed, 

 and occur therefore in both sexes. Others, not quite so perfect, 

 are composed of organs which are sometimes well developed 

 and arranged more or less regularly. These probably develop 

 from the ovary, but just as the stage in which the germ organ 

 is still undifferentiated shades into that in which there is a 

 functional ovary, so no hard and fast line can be drawn between 

 these and included foetuses. Ovarian dermoids which do not 

 make their appearance until later in life undoubtedly arise 

 from the asexual development of ova. There is one long 

 unbroken series of tumours arising from the germ organ and 

 its derivative, the ovary, by the process of direct reproduction, 

 beginning with an organism, that is almost as perfect as its 

 parent, and ending in a shapeless mass of epithelial cells. 

 Just as in the evolution of the race the primitive method of 

 reproduction slowly disappears, leaving here and there behind 

 it evidence of what it once could do, so in the individual this 

 same power, which is so strong in the early embryo, gradually 

 becomes feebler and feebler until it almost dies out. The 

 tumours that grow as buds from the germ organ and its deriva- 

 tives are the expression of so much of the primitive power of 

 direct reproduction as the parent stock retains, set free from 



