1892.] Experimental Embryology. 585 
interrupted here. Killing both left cells of the four, results in 
the formation of larvee which are imperfect in that there is but 
one papilla for attachment and one atrial invagination with 
one pigment spot or eye. Similar monsters result from killing 
both right cells, but the eye spot is absent. 
When three of the four cells are killed the remaining one 
divides normally and forms a rounded mass of cells arranged 
in two germ layers, but the development does not continue 
further. Likewise by thrusting the needle amongst the cells 
of a cleaving egg, though some are killed a few may be sepa- 
rated and then live isolated in the sea water. Such a cell 
divides, with karyokinesis, into two, four, eight cells by planes 
at right angles, then the normal rearrangement and adjust- 
ment of the cells take place as if an entire egg were in ques- 
tion. The cleavage planes also occur at intervals of 20 min- 
utes as in the entire normal egg. There results after some 
hours a rounded mass of twenty or so cells, larger than the 
original one, but there the development ceases. 
In such experiments M. Chabry sees a new method of ana- 
tomical research ; the history of each cell may be followed 
from early to late stages by killing it and observing the conse- 
quent lack in the resulting imperfect later stages. Though it 
is unsafe to conclude from the disappearance of an organ after 
the death of some particular cell at an earlier stage that that 
cell would have formed the organ, yet by killing all the other 
cells, one by one, and finding the organ present in all the 
resulting stages, its dependence in the normal condition upon 
the cell first killed becomes conclusive. In this way the author 
traces the eye to the right anterior cell of the first four of 
cleavage, the otolith to the right posterior cell; the two pa- 
pillee for attachment come from the two anterior cells while the 
chorda is formed by both anterior and posterior cells. Never- 
theless as left-half larvæ are sometimes found with an eye, and 
other such cases occur, the above is upheld by the author only 
by aid of the supposition that the surviving cells change their 
habit after the death of the one, so that they now produce 
organs they would not normally. Thus the eyes are poten- 
tially two, though but the right one is normally produced. 
41 
