KEIMBAHN-DETERMINANTS 233 
contents become visibly different in some animals, 
and when the mature eggs develop normally these 
“organ-forming substances” are segregated in def- 
inite cleavage cells and finally become associated 
with definite organs of the larva. 
Conklin (1905) has shown ‘‘that at least five of 
the substances which are present in the egg (of 
Cynthia) at the close of the first cleavage, viz., 
ectoplasm, endoplasm, myoplasm, chymoplasm, 
and chordaneuroplasm, are organ-forming sub- 
stances.” Under experimental conditions “they 
develop, if they develop at all, into the organs which 
they would normally produce; and, conversely, 
embryos which lack these substances, lack also the 
organs which would form from them.”’ ‘‘Three of 
these substances are clearly distinguishable in the 
ovarian egg and I do not doubt that even at this 
stage they are differentiated for particular ends”’ 
(p. 220). “‘The development of ascidians is a mosaic 
work because there are definitely localized organ- 
forming substances in the egg; in fact, the mosaic 
is one of organ-forming substances rather than of 
cleavage cells. The study of ctenophores, nemer- 
tines, annelids, mollusks, ascidians, and amphibians 
(the frog) shows that the same is probably true of all 
these forms and it suggests that the mosaic principle 
may apply to all animals” (p. 221). The same 
writer has also proved from his study on Phallusia 
(1911) that these various substances exist even when 
they are not visible in the living egg. It is interesting 
also to note that Duesberg (1913) finds the ‘myo- 
