310 ON GROWTH AND OVERGROWTH 



assume a somewhat dubious appearance, they can most assuredly 

 not be regarded (as I find, on reading von Hansemann and other 

 recent writers, I had not been alone in regarding them) as assum- 

 ing a connective tissue type. The nature of the cells forming 

 the chordoma of Ribbert makes him more than doubtful as to 

 the origin of this form of tumour from notochordal remains. I 

 have thus, in deference to his authority, modified to some extent 

 my original statements regarding this. 



The point I wish here to indicate is that mesoblast, " neuro- 

 blast," and notochord are derived from the two primitive cell 

 layers, and the first two at least lose the lining-membrane charac- 

 teristics of these two earliest layers, and take on a less differentiated 

 condition prior to further evolution. 1 At a somewhat later period 

 the mesoblast repeats the process of differentiation, and, from 

 being a simple undifferentiated cell mass which we may compare 

 with the morula, certain of its cells growing outwards between 

 the epiblast and hypoblast become arranged into a definite layer, 

 to form or enclose the primitive body cavity. 2 From this point 

 onwards we can distinguish two structures of mesoblastic origin — 

 the mesothelium, or lining membrane portion of the mesoblast ; 

 and the mesenchyme, or, as I may term it, the mesoblastic pulp. 



It will be seen that I here make no note of the separation of 

 mesoblastic elements into archiblast and parablast, as laid down 

 by His, and made the basis for a classification by Klebs and 

 Williams. His's conception of the parablast, as arising from 

 the elements of the white yolk and from the " granulosa cells," 

 is now known to be wrong, and indeed he has himself withdrawn 

 his earlier hypothesis as to its origin. Add to this, that so hope-* 

 less a confusion has arisen among writers as to what is archiblastic 

 and what parablastic, that we have no option but to discard these 

 terms. As pointed out by Minot, the recognition of the separa- 

 tion of the mesoblast into mesothelial and mesenchymatous 

 elements respectively, suffices for all practical purposes to indicate 



1 [To-day, with all deference to the late Professor Minot's deep knowledge, 

 I would support my original contention that the human notochord, and the 

 chordomas originating therefrom, assume the connective tissue type of cell 

 relationship.] 



a [Even if the body cavity or coelum had its primitive origin as a pouching 

 of the hypoblast, or endoderm lining the enteron, there is, to my knowledge, 

 no clear evidence that in the body cavity of higher animals this is formed other 

 than by a splitting of the mesoblast with subsequent differentiation of the 

 surface cell lining into a mesothelium.] 



