SPIRAL AND RINGED TISSUES

WE have now to consider the Spiral Tissue under another aspect, i.e. that of acting as the internal support of an exterior membrane. Ringed tissues are necessarily conjoined with the Spiral, as they both discharge the same office, and in some cases merge almost imperceptibly into each other in the same specimens. This is most beautifully shown in the proboscis of the common House-fly, to which reference will presently be made.

The subject is so large that only a comparatively small selection of examples can be made, the greater number belonging to Nature, and not to Art.

We will first take the common movable Gas-lamp, with its accompanying tube. It is at present the tube of which we have to treat, the gas itself being reserved for a future age.

It is necessary that, in order to enable the lamp to be moved from one spot to another, the tube through which the gas passes must be so constructed that if it be bent, or even coiled, it retains its form, and does not become flattened. In order to obtain this object, a very long thin wire is coiled spirally to a suitable length. Over this wire is sewn the casing of the tube, which is afterwards made waterproof with elastic varnish. A still simpler mode is by enclosing a spiral wire within a tube of vulcanised india-rubber.