CONSPIRACY AGAINST HAYTI.

There cannot be a doubt that, flushed with their success in the seizure and annexation of Texas, the southern slaveholding banditti are conspiring for the dismemberment of the Haytian republic in the first instance, and its subsequent absorption by this country for slaveholding purposes! They are aiming to establish slavery in Hayti as they have done in Texas. The following letter, which is from a highly respectable source in Washington, is a start-ling character, and renders it highly probable that the conspirators are even among ourselves, on the soil of Massachusetts!

Ipswich, Dec. 29th, 1845.

I casually heard, to-day, that a young seaman of this place, named Leon, had gone up to Boston, to go on a voyage to Hayti. I was anxious to see him; and on inquiry, I learned that he had been offered high wages, $25 per month, by a captain who was fitting out a vessel for Hayti, with the agreement, after the arrival of the vessel there, that they should all serve for the same wages, $25 per month; and it was implied that he was to have very high wages, and it would seem to imply that any bold, daring man might procure very easy high wages, by going out in this vessel. I do not know the name, or whether there is any such vessel fitting out in Boston, for such a purpose, or whether there are any of the Dominicans engaged in fitting out a vessel; but if true, it would seem to imply that there are persons in Boston, who are willing to aid in this conspiracy, and that they are actually fitting out a vessel for this purpose, or are violating the laws of the United States, and may not this be remedied? Is Hayti to be a second edition of Texas? I hope not. I hope that New-England has no citizens who are willing to aid slavery in such a project.

In further proof of the existence of this frightful conspiracy against the freedom and independence of Hayti, read, mark and inwardly digest the extract below, which we copy from the editorial columns of the New-York Herald:—

IMPORTANT NEWS FROM ST. DOMINGO—CONSPIRACY AGAINST HAYTI.

The news which we have received here, during the last two days, by two vessels from different parts of the island of San Domingo, or Hayti, in the West Indies, and which will be found in this day's paper, is of the highest importance to this country and to the world—may, even to the course and progress of Republican government in this hemisphere, for all time to come.

Through the energy and industry of a special agent and correspondent, whom we sent to San Domingo last autumn, we have received, exclusively, copies of several documents and diplomatic correspondence which have already passed between the government of the United States and that of San Domingo, preparing the way for the great measure of the annexation of the latter republic to the former, according to the same policy, or plan, which has annexed Texas; and which must, in a few years, terminated in the absorption or annexation of the latter into this great republic of the North. These documents consist of a report... presented to the United States government at Washington by the agent of Mr. Calhoun to San Domingo, together with copies of highly interesting letters written by various public functionaries in that island, and addressed, during the last summer, to Mr. Hogan, the agent of the United States, sent to San Domingo, to which island he was sent by Mr. Calhoun, then Secretary of State, in order to investigate the condition and ascertain the resources and capabilities of that new republic in the West Indies.

Thus far, the movement has been highly prosperous and successful. The contest between San Domingo and Hayti is rapidly coming to an end, and it is highly probable that the black and mulatto republic will be overcome by the white and more civilized races of the other. As soon as that point shall have been accomplished, there will follow other movements, leading to the natural termination of the whole affair, in the absorption or annexation of both by the United States.

It will be perceived that the diplomatic correspondence which we give, only comes up to the period when Mr. Hogan, the agent, had just left San Domingo. The report which Mr. Hogan has himself made to the Secretary of State at Washington, or the action of our government on that information, we can only as yet conjecture. One thing, however, is certain, that movements, diplomatic movements, of such mighty interest to the destiny of the West Indies, and to the world in general annexation, were not alluded to in the late message of the President to Congress... How far, therefore, the present administration may carry out the views of Mr. Calhoun, we can only conjecture. We have no doubt, however, but Mr. Polk will follow them up, to their full extent. In proof of this, we give below a letter, which we received a few days since, from a gentleman who is favored by God and nature, is surely marching, with rapid strides, to take a place among the nations—that great accomplishment which that great destiny which is allotted to her to fulfill—that is, the union and incorporation, or annexation of Hayti to San Domingo, or a confederation of regular democracies, the whole of Hispanic America, in a short time, and the whole of the trade naturally belonging. In Cuba, in Mexico, in California, and all the rest of Hispanic America, that will, in the course of a few years, lead to the formation of great, free, Anglo-Saxon states. The difference between England and the United States, respecting the 49th parallel in the Oregon boundary, is a mere "flea-bite" compared to the movements contemplated and begun in reference to these millions of square miles, belonging to countries not yet united to this republic. Our government might, to-morrow, settle with Mr. Pakenham, all that England all she asks in Oregon—for less than a quarter of a century—and yet it would be a mere peach, fall into the lap of the United States, along with other territories to which it may be attached. What a magnificent vision of future power, great, and stable government in San Domingo, in Mexico and Oregon, is now opening to our country! The coming events that already cast their shadows over the future, leave no doubt on our mind that the millions of Hispanic race look with favor

MR. HOGAN'S MISSION TO ST. DOMINGO.

To the Editor of the New-York Herald.

The great and important considerations involved in this mission ought not to be lightly overlooked by the country. What are they? They are simply these:—

First—One of the most beautiful and fertile islands in the West Indies, is occupied by a barbarous race, rapidly sinking into a state of savageism, or civil order, a prey to every species of licentiousness and crime, the very details of which would be as monstrous to our sober thinking citizens as Gulliver's travels, or the flights of Baron Munchausen; yet, as true as God is in heaven. They have set aside the ceremonial of marriage, and look upon religion as a farce: and so far have they carried their obscenity, that a majority of the black population, both male and female, go entirely naked, and have not the decency to cover themselves with fig leaves, as our first parents are represented to have done in paradise, after their fall. Can any thing in the organic structure of male and female bodies authorize any one pretending to the least respect for human nature countenance such a state of immorality at our very doors? Surely not.

Secondly—The white inhabitants of Dominico, and those who have fled to other countries, save the honorable position in which these people have placed themselves, to defend their rights, and protect themselves from this oppression, and who have actually taken up arms, and with their own stretched arms to protect them, at least, by their sympathy, from the extermination with which the black population of Hayti threaten them, as they did in the Spanish part of the island.

Thirdly—The interests of humanity in behalf of suffering thousands of our own race and religion, who have been driven from their homes, and forced into the subject, and which, with our government ought to take into consideration, and aid the government, which is seeking redress from the Haytiens for spoliations of the property of French subjects. St. Domingo, thousands of French subjects fled to the United States at the period of the revolution, and become citizens, they, or their offspring, are now living among us, and both humanity and interest, and government may afford them, with other reasons, which might be brought in support of giving the Dominicans our aid, at this moment, when their officers come to us from their government to recognize their independence at once, and open commercial relations with us, or alliance with the white government there. I hope Congress will take up this subject, and examine into it through their hands, while their time is taken up with less important matters. We must have the whole of the paper, standard, or full, this session; and Congress must set in time upon it, before foreign nations step in and take the prize from us.