Variability of shell porosity in the hen’s egg

Abstract does not appear. First page follows.

Introduction

In connection with the formation of the egg in the domestic hen, (Surface (1912)) state that the uterus, which is the shell-forming part of the oviduct, possesses at least two kinds of glands, the function of which is to furnish shell-forming material. From one kind calcerous matter is secreted, from the other mucus. The result is a shell which, according to (Lillie (1919)), consists of three layers, the mammillary layer, the intermediate spongy layer, and the surface cuticle. This heterogeneous envelope is permeable to gases. Lillie explains this characteristic on the basis of a supposed ‘network’ of pores in the spongy layer, connecting the conical inner ends of the mammillae with pores of the cuticle. This conception of shell porosity no doubt originated with (Landois (1865)).

The application of the term ‘spongy’ to the intermediate layer of the egg shell was due to an entirely faulty and misleading experimental procedure. Egg shells were treated with dilute mineral acids. As a matter of course small bubbles of gas, carbon dioxide, appeared scattered all over the exposed shell surface. These bubbles, however, were wrongly interpreted to indicate cavities in the shell and were further assumed to be interconnected by a network of fine channels. Thus, unfortunately, the name ‘spongy layer’ was introduced into ornithological terminology. (Clevisch (1913)), in the course of his much more thorough studies of the subject, found the intermediate layer to represent calcium carbonate crystals, densely knitted together by what appeared to be albuminous material.