1894.] Embryology. 79 
and Hertwig on the one hand and of Roux and Weismann on the 
other. 
tae and Weismann hold that histological differentiation is due to 
qualitative divisions of the idioplasm in successive mitotic cell cleavages 
and that the embryo is thus a mosaic of self-determining cells: more- 
over they assume that each cell may also receive quantitatively some 
unmodified idioplasm that remains dormant till called into activity 
by injury, ete., when regeneration of lost parts is to be accomplished. 
All this Wilson rejects: retaining, however, a modified form of the 
mosaic theory, believing that this principal does come in after the 
earlier stages of cleavage and at very different periods in different ani- 
mals (the differentiation is however a physiclogical one, there being no 
loss of nor unequal distribution of actual idioplosm in cell divisions). 
That the ontogeny is determined by the character of the ovum at 
the first; these first phenomena determine the subsequent ones; the 
prospective value of a cell is a function of its position at first but in 
later stages becomes fixed by internal changes largely due to the ac- 
tion of the whole upon this cell, these are conceptions in which Wilson 
comes into closer agreement with Driesch and Hertwig. 
Experimental Studies on Teleost Eggs.—Dr. T. H Morgan‘ 
claims some very important and valuable results from an application 
of the experimental method to the study of early stages in the em- 
bryology of the fish, Ctenolabrus, Serranus and Fundulus. 
Awaiting the publication of an illustrated paper we can here note 
but a few of the chief facts presented in this preliminary communi- 
cation. 
If one of the first blastomeres is removed and destroyed the other 
may develope a normal embryo which is larger than half a normal 
embryo but not as large as an entire one. 
If half or two-thirds of the yolk be removed from the egg the cleav- 
age is modified and the blastoderm has a peculiar shape yet a normal 
embryo results. 
When the blastodise is compressed so that a flat plate of cells is 
formed by cleavage there yet results a normal embryo. 
Ifthe germ ring be cut upon one side the embryo continues to be 
formed and is normal. It can also be shown by markimg the mem- 
brane with carmine that the head is a fixed point, the elongation of 
the body being posterier to this. Hence it follows that the germ ring 
takes no important part in the formation of the embryo and the con- 
erescence theory receives a very severe blow. 
5Anatomischer Anzeiger. VIII. 1893. 
