114 ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 
crescent and the ectodermal and endodermal areas. The chorda and neural plate 
areas are also visibly different from surrounding areas at this stage (pp. 42, 50, 95, 
97, 98, 108). | 
23. In many cases the cleavage planes do not follow the lines of differentia- 
tion but cut across them. Although cleavage is, under normal conditions, constant 
in form, it is less constant and fundamental than the type of localization, and the 
two are relatively independent (pp. 105, 104). 
24. "The chief factor of localization is protoplasmic flowing; cell division is a 
factor of subordinate value (pp. 102-104). 
25. Experiments which demonstrate the totipotence of blastomeres or regions 
of the egg prove nothing with regard to the presence or absence of differentiation 
in those parts. Some eggs with a high degreee of differentiation have at the same 
time great capacity for regulation, e. g., those of ascidians;! others with no greater 
differentiation have little regulative capacity, е. g., ctenophores and mollusks, 
Therefore the potency of any part of an egg or embryo is no satisfactory measure of 
the degree of its differentiation (pp. 93-95). 
26. Тһе organization of the ovocyte is not the initial organization. Тһе yel- 
low protoplasm (mesoplasm) of the Cyxthza egg is probably derived, at least in part, 
from sphere material (archoplasm) which arose from the nucleus at the last ovo- 
gonic division. The yolk (endoplasm) is formed by the activity of the * yolk 
matrix " (Crampton) which also is probably sphere material. The clear protoplasm 
(ectoplasm) is derived from the germinal vesicle at the first maturation division. Thus 
many important regions of the egg come, at least in part, from the nucleus, and a 
method is thereby suggested of harmonizing the facts of cytoplasmic localization 
with the nuclear inheritance theory (pp. 99-101). ў 
27. There are several distinct types of germinal localization. Тһе annelid- 
mollusk type does not approach that of chordates or echinoderms in the earliest 
stages of localization more closely than in the cleavage or gastrular stages. There is 
no convergence toward a common type in the earliest stages (p. 104-109). 
28. Embryonic repetitions (recapitulations), as well as many other homologies, 
probably result from similarities of egg organization common to each type (p. 109). 
29. “Precocious segregation ” is not a satisfactory explanation of the origin 
of germinal organization (pp. 109, 110). 
30. The evolution of animals must be accompanied by an evolution of the 
type of germinal organization ; modifications of this organization are probably the 
immediate causes of evolution. Transformations which would be impossible in 
adults are readily brought about by modifications in the organization of the egg 
(е. g., inverse symmetry). Perhaps profound mutations or even the origin of dis- 
tinct types may be so explained (pp. 110, 111). 
1 See foot-note p. 95. 
