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Updated: June 23, 2025
Romanes asserts that the lowest order of animals, the annelids, only show traces of fear; a little higher in the scale, in insects, are found social instincts such as industry, combativeness, and curiosity; another step higher, fishes exhibit jealousy, and birds, sympathy; then in carnivorous animals follow cruelty, hate, and grief; and lastly, in the anthropoid apes, remorse, shame, and a sense of the ridiculous, as well as deceit.
There are tentacles and otolith vesicles as very delicate organs of feeling, or possibly of hearing also. But the annelids were probably the first animals to develop an eye capable of forming an image of external objects. The importance of this organ in the pursuit of food or the escape from enemies can scarcely be over-estimated.
How, for example, does it explain the peculiar reproduction which is found to take place in certain marine worms certain annelids?
Then successively those of flatworms, mollusks, annelids, and crabs. All this time the ancestors of vertebrates were swimming in the water above. Food was probably more abundant, certainly more easily and economically obtained by a creeping life, on the bottom. But thither the vertebrate could not go. There his mail-clad competitors were too strong for him.
But even if this were as asserted, nevertheless it fails to explain the peculiar condition presented by Syllis and some other annelids, where a new head is formed at intervals in certain segments of the body. Here there is evidently an innate tendency to the development at intervals of a complex whole.
Fresh-water mussels migrate into deeper water at the approach of cold weather. And if the clam has instincts, there is no reason why the turbellaria should not also possess them. But all higher powers develop gradually, and their beginnings usually elude our search. Along the line leading from annelids to insects instinct is becoming dominant.
This movement is effected, as in the annelids, by the thin blood-vessels themselves, which discharge the function of the heart, contracting and pulsating in their whole length, and thus driving the colourless blood through the entire body.
Its development resembles that from the Annelids to the Vertebrata, the simple canal which constitutes the internal anatomy of the simplest animal forms finding a counterpart in the line of mails vouchsafed by the British postmaster-general to the colonies in 1775 from Falmouth to Savannah, "with as many cross-posts as he shall see fit."
It is probable that we owe almost more on the whole to these unknown but conscientious and industrious annelids than even to those 'mills of God' the glaciers, of which the American poet justly observes that though they grind slowly, yet they grind exceedingly small. In the last resort, then, it is mainly on mud that the life of humanity in all countries bases itself.
There is no a priori improbability in such a belief, for besides other annelids, especially the Arenicola marina, which throws up such a profusion of castings on our tidal sands, and which it is believed thus subsists, there are animals belonging to the most distinct classes, which do not burrow, but habitually swallow large quantities of sand; namely, the molluscan Onchidium and many Echinoderms.
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