x By 1 Wharton: Eggs of Ascaris lumbricoides 21 
completely developed. It will be interesting to determine if 
the eggs of these forms are more resistant to acids or if a dif- 
ference of 3 parts in 1,000, of, say, hydrochloric acid, is suf- 
ficient to stop the development. In weak solutions of formalin 
and of potassium permanganate the embryos also began to 
develop, but died in a few days. The imperviousness of the 
shell is a source of constant surprise. On two occasions ‘the 
uterus of a female containing eggs was left in 3 per cent nitric 
acid over night to fix it for sectioning and later it was found 
that the eggs had divided into 2 cells. 
A small amount of moisture is a necessary requirement for 
the development of the eggs, although drying does not kill them. 
Eggs dry out so quickly on glass plates that they do not begin 
to develop. After fourteen days and again after twenty-one 
days some of them were placed in water; they began to de- 
velop, the first in twenty-four hours and the others in less than 
forty-eight hours. Some eggs were allowed to dry on earth. 
As the earth dried out very slowly most of the eggs began to 
develop. As soon as the eggs became dry the development 
ceased, but began again when the earth was moistened. 
The eggs will not develop without oxygen, although the 
amount needed seems to be very small. If one or two eggs 
in a drop of tap water are sealed in a hanging-drop slide they 
develop as well as when exposed to the air. However, some 
eggs were introduced into water which had been boiled and 
were covered with a layer of oil to prevent the entrance of air; 
none of them had begun to develop after seven days, but they 
did not die as they began to develop as soon as they were placed 
in fresh water. If a large mass of eggs is put into a deep 
narrow dish with a small surface they will not begin to develop. 
I have kept them in this way for a month without results; they 
began their development as usual as soon as they were put into 
fresh water in shallow dishes. 
Temperature undoubtedly has more influence on the devel- 
opment of the eggs than any one other factor. The most 
favorable temperature for development is about 30° C. At 
37° development will begin, but all of the eggs die either in the 
4- or the 8-cell stage. If eggs which have partially developed 
are placed in an incubator at this temperature development 
immediately ceases and they die. Exposure of the eggs to a 
temperature above 37° rapidly causes death. When eggs are 
spread on glass and dipped into water at a temperature of 70° 
_ for five seconds none of them develop. Eggs which contained 
well-developed embryos were placed in tap water at 70° and 
