42 Composition of Eggs. 
should be remembered that they are almost identical. They are 
in fact, equally soluble in the alkalies ; hydrochloric acid dissolves 
them alike, producing the characteristic blue. Before considering 
vitellin and fibrin as identical, we ought to submit vitellin to a 
test which in an unequi vocal manner characterises fibrin. We 
know, after Thenard’s nicer observations, that fibrin has the 
prope rty of decomposing oxygenated water and disengaging oxy- 
gen, like metallic oxyds; the azote obtained from the yellow of 
egg, should decompose oxygenated water, like fibrin, if it were 
identical with the latter. This experiment, —_ several times, 
has always given a negative result. Hence the azote-matter 
which exists in the yellow of bird’s eggs, nod which is precipita- 
ted when the yolk is diffused in a considerable amount of water, 
resents, it is true, an evident analogy to the fibrin of blood, but 
still differs from it in certain characteristics. 
Reviewing the facts as » bird’s eggs, established by us or by 
earlier observers , We may say, that aside from all the zoological 
and anatomical characters “of the shell, its form and its varied 
color, the membranes, thuse formed at the moment of laying the 
egg or those which are developed during incubation,—the two 
essential constituents, prepared by nature to nourish the chick in 
the egg, may always be known by the following characteristics. 
Ist. The white, ety rich in albuminous matter, is plainly sep- 
arated from the yellow by the vitellin membrane. 
_ 2d. The yellow, aie patty made up of phosphuretted fatty 
matter, of a little albumen, of different salts, gives an abundant 
precipitate of vitellin when suspended in enough water. This 
substance, perfectly characteristic of birds eggs, is not met with 
in any other kind of eggs 
2. Eggs of Fishes. 
The extensive family of fish with cartilaginous skeletons, the 
“ Plagiostomes” of M. Duméril, has been divided by recent ich- 
thyologists into many families. The Ray of Linneus and o 
Lacépéde constitute the family Raiide; the torpedos or elec- 
trical fish constitute the family Torpedine ; the race of sharks 
subdivided into many others, is now the family Squalide. In 
the comparative study of these three families in connection with 
ovology, there are found fishes which are oviparous and ovo- 
viviparous. We have mentioned the researches of M. Ch, Ern. 
Baér on the nature of the liquids contained in the egg of the Car- 
tilaginee, where he saw granules which he took for corpuscles of 
albumen. But beyond proving that these grains are different in 
- from ‘conaiie neither he nor other anatomists have 
yet studied the eet the white or of the — the eggs 
of these C: it is a we | have enrne 8° 
a 
