324 ON GROWTH AND OVERGROWTH 



those of epiblastic and hypoblastic origin. The same is true 

 with regard to the tumours of the Fallopian tube. And, so far 

 as I see, we have to lay down also that the high grade of specializa- 

 tion and differentiation of the lining cells of a membrane is 

 accompanied, pari passu, by a lack of capacity to undergo 

 reversion to the simplest type. While, for example, the glial 

 cells are apt to undergo rapid proliferation and form tumours 

 of a simple cellular type, true Neuromata are extraordinarily 

 rare, and in general we may lay down that the high degree of 

 differentiation which has been reached by the neurone has taken 

 from it, to a very large extent, the power of proliferation. This 

 is, it is true, an extreme example. The cells of the uterine 

 mucosa are not nearly so highly differentiated ; they are, how- 

 ever, distinctly more specialized than are endothelia and the 

 cells lining the serous cavities. And, I would add, more 

 differentiated than, for example, the cells of the cortex of the 

 suprarenal, which but attain an arrangement in solid columns 

 resembling that seen during the process of development of certain 

 other glandular organs. 



Thus it may be that simplicity of type is one factor determin- 

 ing why certain tumours revert from a more carcinomatous to 

 a more sarcomatous type. I mention this as a possible factor, 

 and would not dwell too strongly upon it ; rather I would admit, 

 and that willingly, that here we are in the region of analogy and 

 hypothesis. Just as we are unable to explain why in one case, 

 in a given organ, we have produced, for example, a relatively 

 benign adenoma, in another, in that same organ, an actively 

 growing and malignant carcinoma ; so it may be that full con- 

 sideration will show that here also we have to recognize, without 

 possibility of explanation, that, in connexion with tumours of 

 one organ, the lepidic properties are retained with remarkable 

 persistence, while in tumours of another organ, derived from the 

 same cell layer, these same properties are lost with comparative 

 ease. But it seems to me not without its use to point out 

 tentatively a possible factor in the development of the different 

 properties of different tumours. As a group it has to be admitted 

 that mesothelial and endothelial tumours exhibit this tendency 

 to assume a more sarcomatous appearance. 



We are thus justified in separating Lepidomata into two 

 main divisions — the primary lepidomata, wherein we include 



