ON THE DEVELOPMENT OF THE FROG. 289 
The monstrosity consists in (J) the failure of the blastopore to close, 
so that a large persistent yolk-plug is produced ; and (2) the failure of the 
medullary folds to close either (a) throughout, or (3) partially, generally 
in the region of the brain, so that a sort of anencephalous monster 
results. 
With this object the eggs have been grown in solutions whose con- 
centration is isotonic with that of a 0°625 per cent. solution of sodium 
chloride, of the following substances :— 
(1) Chlorides of potassium, lithium, ammonium, calcium, magnesium, 
barium, strontium ; 
(2) Bromides of these seven bases and of sodium ; 
(3) Todides of sodium, potassium, lithium, and ammonium ; 
(4) Sulphates of sodium, lithium, ammonium, and magnesium ; 
(5) Nitrates of sodium, lithium, ammonium, potassium, magnesium, 
strontium, and calcium ; 
(6) Cane sugar and dextrose ; 
(7) Urea. 
The external characters of the embryos produced in these solutions 
have been determined ; the microscopical examination of sections is in 
progress. The results obtained, as far as they can at present be stated, 
are these. The effects produced by the above solutions on the develop- 
ment of the frog may be divided into four classes : 
I. Chlorides of ammonium, strontium, barium, calcium ; bromides of 
ammonium, strontiwm, barium, calciwm, and magnesium, iodides of 
lithium, ammonium, and potassium ; nitrates of ammonium, calcium, and 
strontium. 
In all these the egg dies at a comparatively early stage, sometimes 
auring segmentation, sometimes when the dorsal lip of the blastopore has 
just appeared ; occasionally a very irregular circular lip may be completed. 
The large yolk-cells seem to be affected first, the small animal cells 
continuing to divide for some time ; but as the normal overgrowth of 
cells at the lip of the blastopore is prevented, the roof of the segmentation 
cavity is thrown into folds and wrinkles. Mesoderm cells are formed at 
the equator of the egg, but thrown into the segmentation cavity. 
Ultimately all the cells and their nuclei undergo disintegration and 
degeneration: they are found lying in a coagulum— easily visible to the 
naked eye—produced by the fusion and liquefaction of yolk-granules. It 
seems possible that the salts enter the tissues and there form with the 
carbonic acid given off by the cells insoluble carbonates, as bubbles are 
given off when the eggs are placed in hydrochloric acid. 
II. The egg loses its power of elongating in the direction of the longi- 
tudinal axis of the embryo, that is, remains spherical or nearly so ; 
differentiation of the germ-layers and of the organs of the embryo 
proceeds nevertheless. 
This effect is produced by chlorides of potassium and lithium, bromides 
of sodium, potassium and lithium, iodide of sodium, sulphates of lithiwm 
and ammonium, and nitrates of lithium and potassium. 
In all these a large circular blastopore is formed enclosing a corre- 
spondingly large yolk-plug. This yolk-plug is only very slowly withdrawn, 
if at all. The medullary folds may or may not close. There is variation in this 
1904. U 
