Whilst the country to the north-east of the lakes is mostly composed of rocks, of great age, geologically, such as schists, quartzites, and old doler^^tic rocks, with newer but still ancient trachytes, that to the south-west of them is formed principally of recent volcanic tufas and lavas, the irruption of which has not jet ceased. Most of the land, resulting from the decomposition of the tufas, is of extreme fertility; and, therefore, w^e find on the Pacific side of Nicaragua, indigo, coffee, sugar, cacao, and tobacco growing with the grreatest luxuriance.

Nicaragua is thus divided into three longitudinal zones. The most easterly is covered by a great unbroken forest; the principal products being india-rubber and mahogany. The central zone is composed of grassed savannahs, on which are bred cattle, mules, and horses. It is essentially a pasturage country, though much maize and a little sugar and indigo are grown in some parts. The western zone skirts the Pacific, and is a country of fertile soil, where all the cultivated plants and fruits of the tropics thrive abundantly; the rich, fat land might, indeed, with a little labour, be turned into a Garden of Eden. In the autumn of 187 1, it became necessary for me to proceed to Granada to empower a lawyer there to act for us in a lawsuit in which we were enofaofed. Takino- Velasquez and a servant with me, I rode over to Juigalpa on the I st of November. We had intended to go by land to Granada, but we learnt that, through continued wet weather, much of the low land of the delta of the Malacatoya was impassable, so we determined to make' for the lake, and try to get a boat to take us to Los Cocos, from which place there was a good road to Granada. We found at Juigalpa a Libertad storekeeper, named Senor Trinidad Ocon. He had already engaged a boat, and courteously offered, if we could not find one when we got to the lake, to give us a passage in his. We started from Juigalpa the next morning; and for the first few miles our road lay down by the river, a deep branch of which we crossed. The alluvial plains bordering the river were covered with fine, though short, grass, amongst which were some beautiful flowers. The orange and black " sisitote " {Icterus pcdoralis, Wagl.) flew in

small flocks amongst the bushes; and the '' sanatu " (Qmscalus). was busy amongst the cattle. Their usual plan of operations is for a pair of them to accompany one of the cattle, one on each side, watching for grasshoppers and other insects that are frightened up by the browsing animal. They keep near the head, and tiy after the insects that break cover, but neither encroaches on the hunting ground of the other. We stopped at a little hacienda perched at the top of a small hill. It was called "El Candelera," and was a small cattle station, surrounded by plains. We then crossed the valley, and made for a range of hills between us and the lake. The ascent was steep and rocky; and it took us two hours to get to the top. We then saw the great lake, like a sea lying spread out before us, but still at a considerable distance. The descent was very steep, and we had to make long detours to avoid precipitous ravines. At last we reached level ground; but it was even worse than the mountain roads to travel, being in many parts wet and swampy. After missing our way, and having to retrace our steps for more than a mile, we reached Santa Claro, a cattle hacienda, at dusk. Here we found Seilor Ocon"s boat, but there was no other. The boatmen said we must embark at once. We made an arrangement with a man who had accompanied Ocon to take our mules to San Ubaldo, as we proposed to return that way. The boat was small, and there were seven of us; so that with our saddles and luggage we were much cramped for room.

They poled the boat for two miles down a small river that emptied into the lake, but just before we reached it, the boatmen stopped and said it was too rough to proceed

that night, and notwithstanding our remonstrances they tied the boat to some bushes. Our cramped position was very irksome; the river was bordered by swamps, so that we could not land, and thousands of mosquitoes came about and rendered sleep impossible. About midnight, the moon rose, and two hours later we prevailed on the boatmen to set sail, but, notwithstanding their excuse about it being too rough, there was so little wind that we made slow progress. At eight we went on shore, where there was a hut built close by the lake below Masaya. The lake was flooded, and the water had been over the floor of the hut during the night. All around were swamps, and the mosquitoes were intolerable. We could buy no food at the miserable shanty, and soon set sail again. A little more wind afterwards springing up, we reached Los Cocos at eleven o'clock. There is a small village at this place, where we got breakfast cooked, and did justice to it. We hired horses to take us to Granada; but as the road for a league further on was overflown by the lake, we went on in the boat, and a boy took the horses round to meet us, swimming them across the worst places. Glad we were to get on horseback again, and to canter along a hard sandy road, instead of sitting cramped up in a little boat, with the sun's rays pouring down on us. The path led amongst the bushes, and was sometimes overflowed, but the soil was sandy, and there was no mud. All the beach was submerged, or we should have ridden along it. The last time I had passed by this part of the lake was in July 1868. Then the waters of the lake were low, and we rode along the sandy beach, black in some parts with titanic iron sand. The beach re-

semblecl that of a sea-coast, with the waves rolling in upon it, and to the south-east the water extended to the horizon. Along the shore were strewn shells thrown up by the surf; and on examining them, I found them all to belong to well-known old-world genera Unio, Flanorhis, Ancylus, and Am.puUari.

On this journey, all the beach was, as I have said, covered with water, and I saw no shells; but in the pools on the road were water-beetles swimming about, and these showed a surprising resemblance to the water-beetles of Europe. Gyrinidce swam round and round in mazy circles; Dytiscido' came up to the surface for a moment, aud dived down again to the depths below with a globule of air glistening like a diamond. Amongst the vegetation at the bottom aud sides of the pools Hydro-philidce crawled about, just as in ponds in England. Not only were those familiars there, but they were represented—Gyrinns^byColymhetes,species belongingand Hydroj'iliilus.to the typicalOvergenerathese pools flew dragon-flies, whose larval stages are passed in the water, closely resembling others all over the world. All the land fauna was strikingly different from that of other regions; but the water fauna was as strikingly similar. The sameness of fresh-water productions all over the globe is not confined to animal life, but extends to plants also. Alph. de Candolle has remarked that in large groups of plants which have many terrestrial and only a few aquatic species the latter have a far wider distribution than the former. It is well known to botanists that many fresh-water and marsh plants have an immense range over continents, extending even to the most

;

remote islands.* The close aiBnities of fresh-water animals and plants have been noticed by many naturalists. Darwin saw with surprise, in Brazil, the similarity of the fresh-water insects, shells, &c., and the dissimilarity of the surrounding terrestrial beings compared with those of Britain.t Dr. D. Sharp informs me that water-beetles undoubtedly present the same types all over the world. He believes there is no faTuily of Coleoptcrn in which tropical or extra-tropical species so closely resemble one another as in the Dytiscidcc. Cyhister is found in Europe, Asia, Africa, Australia, New Zealand, Brazil, and North America and the species have a very wide range. Dr. Sharp remarks that this wide distribution and great similarity of the Dytiscidcc is of special interest when "we recollect that they are nothing but Carabidce fitted for swimming, and yet that the Ca rabidce are one of the groups in which the tropical members differ widely from the temperate ones. For following up this branch of inquiry the study of the distribution ofthe raoUusca offers special advantages. There are numerous marine, fresh-water, and terrestrial species and genera. They are slow moving; they have not the means of transporting themselves great distances* like insects, for example, that may easily and often pass over arms of the sea, or fly from one country to another. Their shells are the commonest of fossils; and in islands such as Madeira and St. Helena, where we have abundant remains of extinct land shells, there are few, if any, of extinct animals of other classes or of plants.

Taking the shells of Europe, we find a remarkable * Darwin, " Origin of Species," p. 417. t Ibid., p. 414.

difference in the distribution of the land and freshwater species. According to Mr. Lovell Beeve, who has specially studied this question, out of many hundreds of land mollusks inhabiting the Caucasian province at its centre in Hungary and Austria, only ninety extend to the British Isles, and of these thirty-five do not reach Scotland. Upwards of two hundred species of Clausilia are to be found in the centre of the province, and of these only four reach England, and only one Scotland. Out of five hundred and sixty species of Helix inhabiting the Caucasian province, there are but twenty-four in Britain.

Whilst the distribution of the terrestrial mollusks of Europe is thus restricted in range, though the species are numerous, the fresh-water shells are few in species, but of wide distribution. Quoting again from Mr. Reeve: Of the Lyinim'a-cca '* there are not six species, it may be safely stated, in all Europe, more than there are in Britain. They have no particular centre of creation. There is no evidence to show whether the alleged pro-genitors of our British species were created in Siberia, Hungary, or Thibet. There is scarcely any variation either in the form or number of the species in those remote localities. Of Planorhis scarcely more than fifteen inhabit species the whole eleven of them in Britain."—"Caucasian Ofprovince,Physa andandwe have Lymncea^ it is extremely doubtful whether there are any species throughout the province more than we have in Britain. Neither of Ancylus, which lives attached, limpet-like, to sticks and stones, and has very limited facilities of migration, are there any species throughout the province more than we have in Britain." * * Lovell Reeve, " British Land and Fresh-Water Mollusks," p. 225.

The wide distribution of species inhabiting fresh water compared with those living on land has not, as we have seen, escaped the comprehensive mind of Darwin, and in explanation of the fact, he has shown how fresh-water shells may be carried from pool to pool, or from one river or lake to others many miles distant, sticking to the feet of water-fowl, or to the elytra of water-beetles. Whilst the distribution of water-moUusks may be thus accounted for, the greater variety and more restricted range of the land species is not explained. They have at least equal means of dispersion, compared with the sluggish, mud-loving water-shells of our ponds and ditches. "Why should the one have varied so much and the other so little? We might at first sight have expected the very reverse, on the theory of natural selection. In large lakes and in river systems isolated from others, we might look for the conditions most favourable for the variation of species, and for the preservation of the improved varieties. It is evident that there must have been less variation, or that the varieties that arose have not been preserved. I think it probable that the variation of fresh-water species of animals and plants has been constantly checked by the want of continuity of lakes and rivers in time and space. In the great oscillations of the surface of the earth, of which geologists find so many proofs, every fresh-water area has again and again been destroyed.

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