84 The American Naturalist. [January,. 
the amniotic fluid did not become turbid. Through it each structural 
particular of the embryo and navel cord is easily recognized. The 
temporal artery shows through the transparent skin as a dark brown 
streak, while beneath it is seen the brain through its capsule. In an 
embryo a little larger (30 cm.), the fine hair and hair follicles are 
finely preserved. This last embryo was in a 1:20 solution. 
Experiments with a corpse have not been made, yet the possibility 
of one keeping, may be with safety assumed. In order not to be 
obliged to inject the fluid, it might be necessary to employ the stronger, 
at least 1:10 solution. 
Of the Mammalia, mouse, hamster and porpoise have been left in a 
1:10 solution for over three-fourths of a year. The fluid has not been 
changed and yet remains perfectly clear, while the animals are well 
hardened, unaltered in form and color, and with the hair firmly in 
place. The mammalian eye as well as that of other vertebrates keeps 
better in formol than in alcohol. Still after a time a turbidness appears 
—more in the lens than in the cornea. 
Reptilia and Amphibia preserve well. Frogs, in consequence of the 
. entrance of the fluid into the subdermal space, appear swollen, but in 
other respects are unchanged. 
For fishes, formol especially recommends itself. The mucous and 
slime remain clearly transparent, never forming .the white, stringy 
mass arising in alcoholic preparations. Most fishes retain their colors 
more or lesscompletely. Gold fish, to be sure, loose their color in very 
weak solutions, and the red spots of the trout become white with time. 
A solution diluted 1:10, 1:20, or 1:30, according to the size of the ani- 
mals may be used. In a short time the animals are very nicely har- 
dened. 
From a number of invertebrates I may mention that snails, espe- 
cially slugs, show their form and colors through the transparent 
slime. Insects, spiders and Crustacea preserve at least as well in for- 
mol as in alcohol. 
Living Hiradinea are contracted more in formol than in alcohol; 
at least the contracted specimens are numerous and the extended ones 
few. Thestraw-yellow colors disappear sooner, while, on the other hand, 
orange-yellow, green, brown and black remain unchanged. 
Two jelly fish (Aurelia aurita) killed in a 1:20 solution and kept 
one in a 1:30, the other in a 1:50 solution, were hardened without an 
alteration of form, color, ortransparency. That kept in the 1:30 solu- 
tion is the better, but neither have been long in the fluid. 
