Cuap. II. ALBUMEN AND EGG SHELL. 509 
this solid deposit is found to be composed of a fibrous substance similar to, and 
no doubt identical with, that of the shell membrane, but of a much more tender 
and less dense consistency, (Pl. 9a, fig. 43c,) varying according to the species to 
which the egg belongs. Thus, in Chelydra serpentina it equals about one third the 
thickness of each shelly nodule (fig. 45, @) of which it formed the basis; in Pla- 
typeltis ferox it bears about the same proportion; but im Cinosternum pennsylva- 
nicum it dwindles down to almost one sixth that of its shell, and is much more 
tender and transparent than in the two above-mentioned species, indicating that 
there is far less organic substance for the calcareous deposit in this Turtle than in 
the others. 
In these three species, radiating lines spread out, from the centre of the base of 
the nodule (fig. 45c, 6) toward the surface a, just as in the calcareous state (fig. 
43, a, 6); no doubt impressed upon it by the columnar arrangement of the crys- 
tals of carbonate of lime, which trend in this same direction, as will be seen pres- 
ently. In those shells where the structure is evidently nodular, as in Chelydra, 
(Pl. 9a, fig. 42, 43, a,) the basis, deprived of its lime, still simulates its former shape, 
(43c,) although, as we have said, on a reduced scale; but where the surface of the 
shell is smooth and uniform, as in Cinosternum and Platypeltis, its basis, when 
treated as above, is continuous all over the egg as a wavy stratum, each wave 
corresponding to a group of crystals of carbonate of lime. 
On examining an egg of Chelydra in which the shell is still soft and but very 
little lime has been deposited, we find that the surface of the shell membrane is stri- 
ated by lines running parallel to the axis of the oviduct, and that these lines are 
composed of rows of nodules, (Pl. 9a, fig. 44,) which, upon closer inspection, are 
found to present the characteristic forms in which the crystals of carbonate of lime 
group themselves (fig. 44a). Every little nodule, viewed from the outside, appears 
striated concentrically and radiatingly, each ring between two successive concentric 
strie representing a stratum of crystals, the sides of which are indicated by the 
radiating lines. The centres of crystallization vary in their distances from each 
other: in some instances they are very close together, so that the increasing nodules 
soon press against their neighbors, forming a straight line of contact; in other 
cases, where they are further apart, they retain their globular form much longer. 
Those which are formed early seem to be flattened against each other more 
than those formed later, which fill up the spaces between the original series. 
The earliest indications of these nodules are little, clear, homogeneous, globular 
masses, scattered here and there, which, as they increase in size, begin to show 
faint, radiating, and concentric striw. These stria soon develop themselves strongly, 
so as to be seen without difficulty, as in the nodules which we have described 
as arranged in lines. In fully perfected nodules this striation is quite strong and 
