ground being flooded.

It has often been said that under ordinary circumstances healthy worms never, or very rarely, completely leave their burrows at night; but this is an error, as White of Selborne long ago knew.  In the morning, after there has been heavy rain, the film of mud or of very fine sand over gravel-walks is often plainly marked with their tracks.  I have noticed this from August to May, both months included, and it probably occurs during the two remaining months of the year when they are wet.  On these occasions, very few dead worms could anywhere be seen.  On January 31, 1881, after a long-continued and unusually severe frost with much snow, as soon as a thaw set in, the walks were marked with innumerable tracks.  On one occasion, five tracks were counted crossing a space of only an inch square.  They could sometimes be traced either to or from the mouths of the burrows in the gravel-walks, for distances between 2 or 3 up to 15 yards.  I have never seen two tracks leading to the same burrow; nor is it likely, from what we shall presently see of their sense-organs, that a worm could find its way back to its burrow after having once left it.  They apparently leave their burrows on a voyage of discovery, and thus they find new sites to inhabit.

Morren states [14] that worms often lie for hours almost motionless close beneath the mouths of their burrows.  I have occasionally noticed the same fact with worms kept in pots in the house; so that by looking down into their burrows, their heads could just be seen.  If the ejected earth or rubbish over the burrows be suddenly removed, the end of the worm’s body may very often be seen rapidly retreating.  This habit of lying near the surface leads to their destruction to an immense extent.  Every morning during certain seasons of the year, the thrushes and blackbirds on all the lawns throughout the country draw out of their holes an astonishing number of worms, and this they could not do, unless they lay close to the surface.  It is not probable that worms behave in this manner for the sake of breathing fresh air, for we have seen that they can live for a long time under water.  I believe that they lie near the surface for the sake of warmth, especially in the morning; and we shall hereafter find that they often coat the mouths of their burrows with leaves, apparently to prevent their bodies from coming into close contact with the cold damp earth.  It is said that they completely close their burrows during the winter.

Structure.—A few remarks must be made on this subject.  The body of a large worm consists of from 100 to 200 almost cylindrical rings or segments, each furnished with minute bristles.  The muscular system is well developed.  Worms can crawl backwards as well as forwards, and by the aid of their affixed tails can retreat with extraordinary rapidity into their burrows.  The mouth is situated at the anterior end of the body, and is provided with a little projection (lobe or lip, as it has been variously called) which is used for prehension.  Internally, behind the mouth, there is a strong pharynx, shown in the accompanying diagram (Fig. 1) which is pushed forwards when the animal eats, and this part corresponds, according to Perrier, with the protrudable trunk or proboscis of other annelids.  The pharynx leads into the œsophagus, on each side of which in the lower part there are three pairs of large glands, which secrete a surprising amount of carbonate of lime.  These calciferous glands are highly remarkable, for nothing like them is known in any other animal.  Their use will be discussed when we treat of the digestive process.  In most of the species, the œsophagus is enlarged into a crop in front of the gizzard.  This latter organ is lined with a smooth thick chitinous membrane, and is surrounded by weak longitudinal, but powerful transverse muscles.  Perrier saw these muscles in energetic action; and, as he remarks, the trituration of the food must be chiefly effected by this organ, for worms possess no jaws or teeth of any kind.  Grains of sand and small stones, from the 1/20 to a little more than the 1/10 inch in diameter, may generally be found in their gizzards and intestines.  As it is certain that worms swallow many little stones, independently of those swallowed while excavating their burrows, it is probable that they serve, like mill-stones, to triturate their food.  The gizzard opens into the intestine, which runs in a straight course to the vent at the posterior end of the body.  The intestine presents a remarkable structure, the typhlosolis, or, as the old anatomists called it, an intestine within an intestine; and Claparède [17] has shown that this consists of a deep longitudinal involution of the walls of the intestine, by which means an extensive absorbent surface is gained.

The circulatory system is well developed.  Worms breathe by their skin, as they do not possess any special respiratory organs.  The two sexes are united in the same individual, but two individuals pair together.  The nervous system is fairly well developed; and the two almost confluent cerebral ganglia are situated very near to the anterior end of the body.

Senses.—Worms are destitute of eyes, and at first I thought that they were quite insensible to light; for those kept in confinement were repeatedly observed by the aid of a candle, and others out of doors by the aid of a lantern, yet they were rarely alarmed, although extremely timid animals.  Other persons have found no difficulty in observing worms at night by the same means. [18a]

Hoffmeister, however, states [18b] that worms, with the exception of a few individuals, are extremely sensitive to light; but he admits that in most cases a certain time is requisite for its action.  These statements led me to watch on many successive nights worms kept in pots, which were protected from currents of air by means of glass plates.  The pots were approached very gently, in order that no vibration of the floor should be caused.  When under these circumstances worms were illuminated by a bull’s-eye lantern having slides of dark red and blue glass, which intercepted so much light that they could be seen only with some difficulty, they were not at all affected by this amount of light, however long they were exposed to it.  The light, as far as I could judge, was brighter than that from the full moon.  Its colour apparently made no difference in the result.  When they were illuminated by a candle, or even by a bright paraffin lamp, they were not usually affected at first.  Nor were they when the light was alternately admitted and shut off.  Sometimes, however, they behaved very differently, for as soon as the light fell on them, they withdrew into their burrows with almost instantaneous rapidity.  This occurred perhaps once out of a dozen times.  When they did not withdraw instantly, they often raised the anterior tapering ends of their bodies