EAKTH-WOKMS. 



225 



and leaf-stalks. It requires some manipulation 

 to get these leaves in right, but the worms know- 

 how to perform it, and can discriminate be- 

 tween the easiest way to draw the leaf in and 

 other ways. When they can not obtain leaves, 

 petioles, sticks, etc., with which to plug up the 

 mouths of their burrows, they often protect 

 them by little heaps of stones ; and such heaps 

 of smooth, rounded pebbles may often be seen 

 in gravel- walks. Their strength is shown by 

 their often displacing stones in a well-trodden 

 gravel-walk, a task that sometimes demands 

 considerable effort. 



Worms excavate their burrows in two ways : 

 by pushing away the earth on all sides where 

 the ground is loose or only moderately com- 

 pact, and by swallowing the dirt, where the 

 ground is hard, and ejecting the swallowed 

 earth afterward in the form of the "castings" 

 which are found at the mouths of their bur- 

 rows. They also swallow the earth to extract 

 the nutritious mutter which may be contained 

 in it, and in larger quantity than for making 

 their burrows ; and the residue of this, after 



Fio. 2. A TOWER-LIKE CASTING. PROBABLY EJECTED BY 

 A SPECIES OP PERICH^ETA (from the Botanic Garden, 

 Calcutta : of natural size, engraved from a photo- 

 graph). 



the nutriment is extracted, is also cast out. 

 The deposition of castings is no insignificant 

 part of the labor that they perform, and leaves 

 very perceptible traces on the surface. The 

 VOL. xxi. 15 A 



castings may be seen in garden-walks piled up 

 in towers of greater or less height around the 

 burrows. The towers formed by a naturalized 

 East Indian worm, at Nice, France, which are 

 sometimes distributed as thickly as five or six 

 to a square foot, are built to a height of from 

 two and a half to three inches. The tower of 

 a perichaeta in the Botanic Garden of Calcut- 

 ta, of which Fig. 2 is an exact representation, 

 measured three and a half inches high and 1*35 

 inch in diameter. 



Some of the towers, as the figure shows, 

 exhibit a considerable degree of skill in their 

 construction. The castings are not always 

 ejected on the surface of the ground, but are 

 often lodged in any cavity that may be met in 

 burrowing. The burrows run down, some- 

 times perpendicularly, generally a little ob- 

 liquely, to a depth of three, six, and even eight 

 feet, and are usually lined with a thin layer or 

 plaster of fine, dark-colored earth which the 

 animals have voided, in addition to which a 

 lining is made, near the mouths, of leaves, also 

 plastered. Bits of stones and seeds are also 

 sometimes found in the bottom of the burrows, 

 having been taken down apparently with a 

 purpose. 



The amount of earth brought up by worms 

 from beneath the surface has been carefully 

 estimated by observing the rate at which 

 stones and other scattered objects on top of 

 the ground are buried. A piece of waste, 

 swampy land, which was inclosed, drained, 

 plowed, harrowed, and thickly covered with 

 burned marl and cinders, and sowed with 

 grass, in 1822, fifteen years afterward pre- 

 sented the appearance, where holes were dug 

 into it, shown by Fig. 3, the scale of which is 

 half that of nature. Beneath a sod an inch 

 and a half thick was a layer of vegetable mold, 

 free from fragments of every kind, two and a 

 half inches thick. Under this was another 

 layer of mold, an inch and a half thick, full of 

 fragments of burned marl, fragments of coal- 

 cinders, and a few white-quartz pebbles. Be- 

 neath this layer, and at a depth of four and a 

 half inches from the surface, the original black, 

 peaty, sandy soil with a few quartz pebbles 

 was encountered. Six and a half years after- 

 ward this field was re-examined, and the frag- 

 ments were found at from four to five inches 

 below the surface, having been covered in that 

 time with an inch and a half more of mold. 

 The average annual increase of thickness for 

 the whole period was '19 of an inch. This was 

 less than the average increase of thickness in 

 some other fields similarly observed, in which 

 the accumulation amounted to '21 and '22 of 

 an inch annually. Another field, which was 

 known as "the stony field," and in which the 

 stones lay so thick that they clattered as one 

 ran down the slope of the hill, became so 

 covered with mold in thirty years that a horse 

 could gallop over the compact turf from one 

 end of the field to the other, and not strike a 

 stone with his shoes. A flagged path in Mr. 



