518 Edwin G. Kirk. 
each new generation and are available, if altered conditions make 
it desirable or imperative that they should become dominant. 
This view of the morphologic flexibility of ‘‘specialized”’ cells, 
under changed conditions will be recognized as O. Hertwig’s 
doctrine of the nature of cell specialization, under a slightly 
different guise. But this conception is also expressable in terms 
of Weismann’s Keim-plasma theory, provided sufficient emphasis 
be laid on the accessory Keim-plasms. 
It seems probable that the mucigenic character of the large 
proportion of cardiac mucus cells;—namely, those derived from 
the mucus cells of the foveolar and cervical segments of the old 
left fundus glands, is palingenetic. On the other hand, it is prob- 
able that some of the deeply situated mucous cells are coenogen- 
etically mucous, having passed, in race history, through the zymo- 
genic or parietal stages. 
The temporary occurrence of zymogen in the deeper mucous 
cells seems to indicate this, and to suggest that here the reserve 
zymogenic characters have not yielded, without a struggle, to 
the mucigenic, the old dominance of the zymogenic having become 
through the habit of ages, too strongly impressed on the cell 
metabolism to be rapidly effaced by the coenogenetic dominance 
of the mucous characters. 
Bensley (00) found, in the developing of gastric glands of 
Amblystoma, cells which contained for a brief period, both zymo- 
genic and mucigenic granules. Thus it seems that sometimes, in 
the embryonic and possibly in the adult stages,—the cell meta- 
bolism may be controlled by two distinct sets of determinants,— 
through the manifestation of either of which we are ordinarily 
inclined to consider a cell as ‘‘specialized.’’ Such instances seem 
to be uncommon, and it is probable that sooner or later,—one 
metabolic complex takes a subordinate place,—at least in the 
metazoa. 
The fate of the cardiac parietals, after birth, promises to be of 
the greatest interest in this connection, as there are only two 
possibilities open to these cells —degeneration, or conversion into 
mucous cells, 
