880 The American Naturalist. [October, 
about the equator of the egg, where the long diameters of the 
areas are parallel to the long diameter of the egg, an arrange- 
ment due in part to a conformation of the areas to the curva- 
tures of the surface, and in part to the structure of the fibrous 
shell. Calcareous deposit is most abundant at the poles of the 
eggs, and wherever two shells come in contact, they are firmly 
cemented together by the same material, all of which usually 
adheres as an elliptical area to one of the shells, when two 
thus joined are forcibly pulled apart (Fig. 1, a). 
The shell is wonderfully tough for its thickness, which is 
only from 5 — mm., made up, except for the superficial de- 
posit of mineral matter, entirely of highly elastic fibres resem- 
bling in their disposition to curl when broken, and their neu- 
tral reaction to acetic acid, the yellow elastic connective 
tissue fibers. These vary somewhat in thickness, the largest 
having a diameter of zi; mm., the smallest of sis mm., 
and the bulk of 51; mm. They are extremely long, and I 
rarely found an end not artificially made. Naturally, they 
seem frequently to terminate in ovoidal or cylindrical swell- 
ings which are often sharply twisted, bent or folded. Unlike 
those which form the shell of bird's eggs, these fibres branched 
but very rarely, although short filamentous processes were not 
infrequently seen attached along their sides. Several fibres 
were traced under the microscope for an inch of their lengths 
without a single branching being detected. Two or more fibres 
frequently run side by side for long distances, and separating, 
give rise to a deceptive appearance of branching. 
The most interesting fact to be noted with regard to the 
structure of the fibres is that they are tubular. Most, if not 
all of them, possess a distinct and continuous lumen, having 
a diameter of from 3 to 1 that of the entire fibre. This struc- 
ture is well-shown in cross section (Fig. 3), and perhaps even 
more strikingly in specimens which, after having been allowed 
to dry, are mounted in glycerine, when the lumen becomes 
very conspicuous from the chain of minute air-bubbles which 
fill it and mark its course as a dark beaded line (Fig. 4). 
The mannerin which the egg-shell is built up out of these 
fibres is strikingly different from what obtains in the mem- 
PEE PEE e WARD a NETS EA DR 
