28 Indications of Continued Formative Influence 
are sent out from this zone, they conduct themselves in 
a quite indifferent way, though for a greater or less time 
they preserve their germinative capacity potentially. 
While the experiments of Roux carried on carefully 
and with astonishing exactness of observation, dem- 
onstrate directly the continued remote and mediate action 
which the formative part exercises upon the part being 
formed throughout the whole of development, the exist- 
ence of this action is confirmed by other investigations, 
in a way which though indirect is not any less certain 
on that account. 
They comprise all the cases in which the part removed 
is regenerated by cells histologically different from those 
of normal generation, for instance in which organs or 
tissues of ectodermic, mesodermic, or entodermic origin 
are reproduced in the regeneration by tissues having a 
different blastodermic origin. 
It will suffice for our object to recall the most typical 
example which has stirred up the two hostile camps of 
the epigenesists and the preformists; we refer to that 
of the regeneration of the lens in the eye of the tritons, 
which, after its extirpation, is reproduced from the cells 
of the iris, that is to say, from a material quite different 
in character from that of which it is formed in normal 
generation.® 
The double epithelial layer of the iris, from the 
marginal proliferation of which the new lens springs, 
must exercise upon the lens in process of formation a 
continuous action persisting throughout the development 
®See ve. g. Erik Miller: Uber die Regeneration der Augenlinse 
nach Exstirpation derselben beim Triton. Archiv f. mikrosk. Anat. 
und Entwicklungsgesch. Band, XLVII. erstes Heft. Bonn. Cohen, 
1896. P. 23 ff., especially 29 and 30. 
