THE GROWTH OF THE EMBRYO IN THE FROG. 
243 
April 3. Each egg has formed an embryo, and in each instance with the head to 
the side of the egg touched. 
Obs. 2. — Four eggs were placed in separate cells as before, and only two became 
fruitful. 
In one the primary cleft was in the precise line of the spot touched, although the 
egg subsequently diverged to the left; and the head corresponded to the part fecun- 
dated. In the other egg the cleft was about ten degrees to the left of the part im- 
pregnated, and the head was also turned to the part touched with the fluid. 
Obs. 3. — Four other eggs were taken, but two of them were sterile; and in the 
development of one the head deviated remarkably from the usual position. 
The first cleft in one (a) was about six degrees to the right ; and in the other ( b ) 
about five degrees to the left of the point touched. Both formed embryos : in one 
(a) the head was at the end of the cleft nearest the point touched, but in the other ( b ) 
at the end furthest from the same point. The peculiarity in this last experiment I 
cannot explain ; possibly there might be some want of precision in conducting it. 
Similar experiments were repeated four other times, and the results showed that 
the first cleft of t he yelk is in a line with the point of the egg artificially impregnated, 
and that the head of the young frog is turned towards the same point. But in this 
set, as in the other, the nascent being in the course of its development deviated to 
the right or the left of a line through the centre of the spot fecundated. 
In another set of experiments the spermatic fluid was applied to an unknown part 
of the egg. 
On taking my last female frog (April 5, 1853) I found the white part so dark in 
colour (not a very unusual change), that the usual black surface could not be well 
distinguished. Accordingly the eggs were put into separate cells, and the fluid was 
applied and the cell marked in the usual way, without a knowledge of what was the 
spot touched. 
Experiment 1. — Six eggs were used : all were fecundated, and segmented in about 
three hours and a half in an atmosphere varying from 61° to 64° Fahr. The follow- 
ing is the result : — 
The axis of the embryo was in one in a line with the part touched, in four diverging 
slightly to the left, and in one to the right of that line. The head was in four nearest 
to the spot fecundated, and in two furthest from it. 
Experiment 2 with five eggs : all of these were fruitful. The axis coincided exactly 
with the impregnated point in three, and diverged slightly to the left in two eggs. 
The head was nearest the same point in four, and furthest from it in one embryo. 
Experiment 3.— Five eggs were employed, and being fertilized, gave the following 
result : — 
The axis coincided with the given point in one, and diverged more to the right or 
left in the other instances. The head was nearest the side to which the spermatic 
fluid was applied in four, and furthest from it in one. 
2 i 2 
