25 
upon the ventral surface, and almost directly opposite the 
point where the primitive mouth was situated at an earlier 
stage. The digestive cavity now becomes greatly enlarged, 
and cilia make their appearance upon its w T alls, the mouth 
becomes connected w T ith the chamber which is thus formed, 
and which becomes the stomach, and minute particles of 
food are drawn in by the cilia, and can now be seen inside the 
stomach, where the vibration of the cilia keep them in con- 
stant motion. Up to this time the • animal has developed 
without growing, and at the stage shown in Figure 36 
it is scarcely larger than the unfertilized egg, but it now 
begins to increase in size. The stages shown in Figures 44 
and 45 agree pretty closely with the figures which European 
embryologists give of the oyster embryo at the time when it 
escapes from the mantle chamber of its parent. The Ameri- 
can oyster reaches this stage in from twenty-four hours to six 
days after the egg is fertilized ; the rate of development be- 
ing determined mainly by the temperature of the water. 
Soon after the mantle has become connected with the stom- 
ach, this becomes united to the body wall at another point a 
little behind the mantle, and a second opening, the anus\ 
is formed. The tract which connects the anus with the stom- 
ach lengthens and forms the intestine, and, soon after, the 
sides of the stomach become folded off to form the two halves 
of the liver, as shown in Figure 44. 
Various muscular fibres now make their appearance within 
the body, and the animal assumes the form shown in Figures 
44 and 45. 
All my attempts to get later stages than these failed, through 
my inability to find any way to change the w T ater without 
losing the young oyster, and I am therefore unable to describe 
the manner in which the swimming embryo becomes con- 
verted into the adult, but I hope that this gap will be filled, 
either by future observations of my own or by those of some 
other embryologist. 
In my attempt to raise the oyster embryo from the egg, I 
found that continuous warm weather was essential to success. 
