THE INFLUENCE OF SALT AND OTHER SOLUTIONS ON THE FROG. 179 
duced by this solution are then due entirely to its capacity of withdraw- 
ing water that is needful for development. 
2. Other solutions—those of the first class—are toxic in virtue of 
some other property, though what this is is unknown. 
3. The same may be said of the solutions of the second class. 
4. In the case of the chloride, nitrate and bromide of sodium, the 
chloride, nitrate and sulphate of magnesium, the increased osmotic pres- 
sure may play some part, though it certainly is not responsible for the 
whole effect. Cane sugar may be best associated with these. 
5. The behaviour of those eggs which remain spherical though dif- 
ferentiation continues is probably not to be put down to the increased 
osmotic pressure alone ; these embryos are quite unlike the dextrose 
embryo. It seems more likely that the substances enter the ovum, and 
there interfere with processes (? proteolytic fermentations) that would 
normally result in the production of substances with a higher osmotic 
pressure than, and capable of absorbing water from, the medium. That 
potassium chloride, for example, does penetrate the tissues is proved by 
the liquefaction of yolk-granules which occurs in this solution. 
Finally, there remains to be described the effect of more concentrated 
solutions of substances—urea and sodium sulphate—which are known to 
penetrate the embryonic tissues, but in the strengths employed before 
were harmless. 
Sodium Sulphate.—The solutions employed were : (1) 1°16 per cent. 
(this is the original concentration) ; (2) 1°325 per cent, ; (3) 1-54 per cent. ; 
(4) 1°85 per cent. ; (5) 2°32 per cent. ; (6) 2°5 per cent. ; (7) 3 per cent. ; 
(8) 3:5 per cent. ; (9) 4 per cent. 
(1) Development is normal. 
3} The brain and blastopore may both remain open ; the open brain 
degenerates and becomes grey. Internally there is considerable differentia- 
tion ; nerve-fibres are developed in the spinal cord, the eye—retina, cho- 
roid fissure, lens—is normal, the heart is bent, there are three pronephric 
funnels, and the peritoneal cavity is large. The stomodeum is, however, 
still closed at the time when the larva dies. 
(3) Much as the last, but the optic cup is not quite normal and the 
lens is solid. 
(4) The tail is very short and the fin badly developed. Internally the 
peritoneal cavity is not developed, and the gut lumen is very narrow. 
(5) The tail is shorter still, and the medullary groove is open and grey 
throughout. This embryo resembles a typical sodium chloride monster. 
The heart is solid, and there is only one pronephric funnel. 
(6) Externally this resembles the last.. Internally the pericardium is 
smaller, the gill-slits are absent, and there is only a pronephric ridge—no 
tubules. The notochord is still vacuolated. 
(7) In this solution degeneration sets in at a much earlier stage. The 
yolk-plug is very large; the medullary folds are formed and become 
grey ; below what appears to be the dorsal lip of the blastopore is a 
grey zone between the lip and the white yolk-plug. Sections, however, 
discover the interesting fact that the lower margin of this grey zone is 
in reality the blastoporic lip, and is separated from the yolk by a slight 
indentation. The apparent blastoporic lip is the rim of an aperture lead- 
ing into an archenteric cavity, as it must be called, since notochord and 
N 2 
