of which it was very fond-before eating them. But this habit is by no means common to all birds; some kinds are actually known to swallow living snails, and Mr. Cordeaux has favoured me with his opinion that in all probability the creatures frequently keep alive for some little time after being swallowed; and on this point, fortunately, an observation of much interest has been recorded, the accuracy of which, Mr. Roberts, of Lofthouse, assures me, cannot be doubted. In September, 1875, it appears, Mr. John Ward, carpenter and bird-stuffer, of Lofthouse, took thirteen wrinkled-snails (Helix caperata), together with a quantity of tares, from the stomach of a wood pigeon which had been shot three days previously. Most of the snails were alive, and began creeping about on being placed in a dish containing a little water." It may be mentioned, as a somewhat analogous case, that Mr. Abel Chapman has frequently shot curlews stuffed with live cockles, which, as he remarks, might easily have been scattered if the birds had chanced to have been killed and carried off by peregrines or other birds of prey. Molluscs thus remaining alive in birds' crops,

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1 Mr. Roberts informed me of this fact, without comment, in 1890, but recently, after drafting this chapter, I was much pleased to find that when recording it, in 1882, he had suggested that molluscs might possibly be "carried in the crops of birds considerable distances, and thus be distributed and established in new districts, or on islands, as the living shells might be ejected from the crop, or the birds might be killed by birds of prey and the contents of the stomach dislodged and scattered."-" "Topography and Nat. Hist, of Lofthouse," 1882, p. 333.

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as Mr. Darwin's remarks suggest, may possibly be transported, especially during gales, under exceptionally favourable circumstances, to new homes perhaps several hundreds of miles from their original habitats. At ordinary times birds often fly a long way to feed-wood pigeons, for instance, do so when necessary-and if struck down by birds of prey when returning home, the living contents of their crops might possibly be liberated at considerable distances from the feeding-ground. There is no actual proof, as far as I know, that shells have ever been scattered from crops in the manner here indicated, but an observation of much interest in this connection has been made by Mr. Aplin, who tells me that he once noticed a little heap of barley, evidently carried from a distance, lying among the remains of two wood pigeons which had been killed by a hawk, probably a peregrine. Even when a snail-eating bird happens to be killed on its feeding-ground, the bird of prey, soaring across hill and dale" to a hiding-place, and carrying its victim with it, might ultimately scatter a few snails miles from their original home; it may be remarked, however, as Mr. Aplin points out, that except in the breeding season when they have young, hawks, etc., often or usually eat their kills on the spot, or close to it; but it is undoubtedly probable, as Mr. Cordeaux assures me, that both seeds and shells have been distributed, to some extent, by hawks, owls, etc. sometimes devouring their victims at a distance from where they were struck down. It seems possible, also, that snails in the crops of dead birds may be floated, at rare

intervals, on the surface of the ocean, to be ultimately liberated, perhaps, on some distant shore. Large numbers of land-birds, I suppose, annually perish in the sea; their floating carcases, Darwin states, sometimes escape being immediately devoured,' and, as shown by Mr. Ward's observation, a Helix can retain life in the crop of a dead bird at least for three days. In such circumstances, of course, molluscs would be protected to some extent from the evil influences of salt water, and, in illustration of this point, it may be noted that a number of seeds of peas and vetches (which are killed by a few days' immersion in sea-water) nearly all germinated after having been enclosed in the crop of a pigeon which had floated on artificial sea-water for thirty days.2

Various kinds of birds, it will be remembered, have been observed to eject the contents of their crops when frightened or wounded, as gulls and terns do when pursued by the skuas, and it seems quite possible, as Mr. Roberts has already suggested, that snails, still alive, may occasionally be thus disgorged, and set down in places perhaps some considerable distance from the spot where they were picked up and swallowed. Mr. Clement Reid suggests that a good deal may have been done, also, by birds gorging themselves after a long and wearying migration, and afterwards casting up the contents of their stomachs, little injured, and perhaps a considerable distance away, and he states that he has

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"Origin," p. 326.

2 "Origin,” p. 326.

several times come across castings of this kind, containing soft seeds, live worms, etc.

It must be borne in mind, of course, that the transportal of shells by these agencies to distant points over the ocean can only very rarely happen, but, as Mr. Wallace has remarked, "nature can afford to wait," and if but once in a thousand years, he adds, “a single bird should convey two or three minute snails to a distant island, this is all that is required for us to find that island well stocked with a great and varied population of land-shells." We must remember, however, that resulting colonization is much more rare than mere transportal, though, of course, snails carried by birds into the interior of new countries or islands, or to some little distance inland, are more likely to be able to establish themselves than are those stranded upon the shores with drift-timber, etc. The creatures are carried, we may feel sure, for comparatively short distances within given tracts of land much more frequently, and many apparent anomalies in local distribution no doubt have thus arisen, but even here the ultimate establishment of a new colony seems likely to be a rare event. Additional ways in which short migrations may possibly be brought about might be referred to. Small shells, such as those of the genus Vertigo, and eggs of various kinds must occasionally happen to be adhering to twigs, etc., carried off by birds when building, and these are sometimes collected at some little distance from the nest; every one, no doubt, remembers having seen rooks "Geographical Distribution," i. p. 32.

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flying overhead with twigs in their mouths. A living specimen of Limnæa truncatula-the "ditch mud-shell" of Gray's Turton-once found, as the reader will remember, on the top of a church in Preston, had very probably been carried there, as Mr. Heathcote suggests, adhering to one of the sticks taken up by a jackdaw building in the tower. Thrushes, red-wings, etc.—great snail-eaters-as Mr. Cordeaux remarks to me, will carry shells to considerable distances, and from being disturbed or otherwise may sometimes drop them, or neglect to break them against their favourite stones, and Mr. Roberts, I hear, has actually seen a thrush drop a snail while flying. Quite recently, I found on a snowcovered road in Lincolnshire-a hibernating snail, Helix aspersa, which, having a pierced epiphragm, had almost certainly been carried and dropped by a bird. No stones on which shells had been broken were near, but several were seen at some distance along the same road. On being placed in tepid water the snail revived, and crawled away.

Operculate land-shells, it seems probable, may occasionally be carried in the manner already suggested for operculate pond-snails in chapter iv., namely by closure of the operculum, so as to hold on to the toes of insects, etc. As there mentioned, a land-shell has been seen holding on to a humble-bee in this way. The observation referred to was made in June, 1885, and recorded in the Field in that year.' The

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1 F.W.T.," Humble-bee trapped by snail," "Field," lxv. (1885), p. 843.