"So, naturalists observe a flea
Has smaller fleas that on Lira prey;
And these have smaller still to bite 'em,
And so proceed, ad infinitum."
The variety of animal food is, therefore, as broad as animated nature. Hence, we find great variety of means and methods for procuring subsistence. Particularity in food implies especial or efficient means of getting that food. The strange appendages of animals, their form, color, and habits, have to do more with the prehension of food than with any other function. It will be interesting to briefly survey the animal kingdom with reference to this marvelous adaptation. Its origin we will not discuss.
The simplest manner of procuring food is shown by the tapeworm and some other intestinal animals. These feed on the nutritive fluid prepared in the alimentary canal of the animals which they inhabit; and, being destitute of mouth and stomach, absorb the already digested food directly through the skin or body-walls. Probably this absorption does not require will or effort on the part of the parasite, but takes place simply by the physical action known as osmose. It is thus equivalent to the last step in the digestive process of higher animals. Some parasites, as the larva of the tapeworm, which live in the muscles and tissues, imbibe the animal juices by the walls of the body; but here the process as a whole is slightly higher, for this food probably requires more elaboration or digestion.
Fig. 1.—Hawk-Moth (Sphinx quinquemaculatus).
Any special modification or organ for procuring food is a great advance beyond the method already described. Liquid food is more easily prehended than solid, yet the means are various and remarkable. Even the simplest organs are wonderful in their structure and action.
Those butterflies and moths which take any food at all have a
